<DOCUMENT>
<TYPE>EX-99.12
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<FILENAME>ex99-12.txt
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                                                                   Exhibit 99.12


                            FSP ADDISON CIRCLE CORP.

                  SUPPLEMENT TO CONSENT SOLICITATION/PROSPECTUS

      This Supplement is to supplement the Consent Solicitation/Prospectus being
furnished to holders of preferred stock in four real estate investment trusts,
FSP Montague Business Center Corp., FSP Addison Circle Corp., FSP Royal Ridge
Corp. and FSP Collins Crossing Corp., each of which is referred to as a target
REIT. The Consent Solicitation/Prospectus and this Supplement thereto are being
furnished in connection with the solicitation of votes to approve an agreement
and plan of merger, dated August 13, 2004, by and among Franklin Street
Properties Corp., referred to as FSP Corp., four wholly-owned acquisition
subsidiaries of FSP Corp., referred to as the acquisition subsidiaries, and the
target REITs. The merger agreement provides for the acquisition of the target
REITs by FSP Corp. by merging each of the four target REITs with and into a
related acquisition subsidiary.

      As the effects of the mergers may differ for stockholders in each of the
target REITs, a supplement similar to this Supplement has been prepared for each
of the target REITs. We are providing you and every stockholder in each of the
other target REITs with all the Supplements prepared for the target REITs.

Risk Factors

      In evaluating the mergers, you should carefully consider the following
factors, which are described in detail in the section of the Consent
Solicitation/Prospectus entitled "Risk Factors," in addition to other matters
set forth in the Consent Solicitation/Prospectus.

Risks Relating to the Mergers

      o     The nature of the target REIT stockholders' investment in their
            respective target REITs will change upon consummation of the
            mergers.

      o     The mergers may affect the level of dividends paid to target REIT
            stockholders.

      o     Target REIT stockholders will be foregoing the potential
            appreciation in the real property owned by their respective target
            REIT.

      o     The future price of FSP common stock may be lower than the price per
            share negotiated for purposes of the merger consideration.

      o     The mergers will require the target REIT stockholders to forgo
            alternatives to the mergers.

      o     Target REIT stockholders will experience a loss of relative voting
            power.

      o     The target REIT stockholders will experience greater risks relating
            to diversification of portfolios following the mergers.

<PAGE>

      o     The officers and directors of the target REITs have conflicts of
            interest that may have influenced them to support or adopt the
            merger agreement.

      o     The combined company may be liable for contingent or undisclosed
            liabilities of the target REITs.

      o     The shares of FSP common stock received by the target REIT
            stockholders are not tradable on a national stock market or other
            exchange.

      o     The target REIT stockholders may experience dilution of their
            respective holdings in FSP Corp.

      o     A majority vote of the target REIT stockholders of a target REIT
            will bind all the target REIT stockholders of that target REIT.

      o     Following consummation of the mergers, the combined company may no
            longer qualify as a REIT

Real Estate and Business Risks of FSP Corp.

      o     If FSP Corp. is not able to collect sufficient rents from each of
            its owned real properties, FSP Corp. may suffer significant
            operating losses or a reduction in cash available for future
            dividends.

      o     FSP Corp. faces risks in continuing to attract investors for
            sponsored REITs.

      o     If FSP Corp. is unable to fully syndicate a sponsored REIT, it may
            be required to keep a balance outstanding on its line of credit or
            use its cash balance to repay the line of credit, which may reduce
            cash available for distribution to FSP stockholders.

      o     FSP Corp. may not be able to find properties that meet its criteria
            for purchase.

      o     FSP Corp. is dependent on key personnel.

      o     FSP Corp.'s level of dividends may fluctuate.

      o     The real properties held by FSP Corp. may significantly decrease in
            value.

      o     New acquisitions may fail to perform as expected.

      o     FSP Corp. faces risks in owning and operating real property.

      o     FSP Corp. faces risks from tenant defaults or bankruptcies.

      o     FSP Corp. may encounter significant delays in reletting vacant
            space, resulting in losses of income.

      o     FSP Corp. faces risks from geographic concentration.


                                       -2-
<PAGE>

      o     FSP Corp. competes with national, regional and local real estate
            operators and developers, which could adversely affect its cash
            flow.

      o     There is limited potential for an increase in leased space gains in
            FSP Corp.'s properties.

      o     FSP Corp. is subject to possible liability relating to environmental
            matters, and FSP Corp. cannot assure you that it has identified all
            possible liabilities.

      o     FSP Corp. is subject to compliance with the Americans With
            Disabilities Act and fire and safety regulations which could require
            FSP Corp. to make significant capital expenditures.

      o     There are significant conditions to FSP Corp.'s obligation to redeem
            shares of its common stock and any such redemption will result in
            the stockholders tendering shares receiving less than their fair
            market value.

      o     FSP Corp. may lose capital investment or anticipated profits if an
            uninsured event occurs.

      o     Contingent or unknown liabilities acquired in mergers or similar
            transactions could require FSP Corp. to make substantial payments.

      o     FSP Corp. would incur adverse tax consequences if FSP Corp. failed
            to qualify as a REIT.

      o     Provisions in FSP Corp.'s organizational documents may prevent
            changes in control.

      o     The trading price of FSP common stock following listing on the
            American Stock Exchange or other national security exchange is
            uncertain. The FSP common stock could trade at a lower price than
            anticipated.

Effects of the Mergers

      Pursuant to the merger agreement, FSP Addison Circle Corp., or Addison
Circle, will merge with and into a wholly-owned subsidiary of FSP Corp. called
Addison Circle Acquisition Corp. and created for the sole purpose of the merger,
with the acquisition subsidiary as the surviving corporation. The stockholders
of Addison Circle will be issued shares of FSP common stock which will be
registered under the Securities Act of 1933, as amended, on a registration
statement on Form S-4 to which this Supplement is an exhibit. As a result of the
mergers, Addison Circle preferred stockholders will exchange their interests in
Addison Circle, a real estate investment trust organized as a Delaware
corporation, for interests in FSP Corp., a real estate investment trust
organized as a Maryland corporation.

      There are significant differences between Addison Circle and FSP Corp.,
including the following:

      o     FSP Corp.'s real estate portfolio will be substantially larger and
            more diverse geographically, by property type and by tenant
            business;


                                       -3-
<PAGE>

      o     FSP Corp.'s business will generate revenues from real estate
            investment banking/brokerage and property management activities and
            from a larger and more diversified real estate portfolio;

      o     The nature of each Addison Circle preferred stockholder's investment
            will change from an interest in a corporation owning a specified
            property for a finite period in which the Addison Circle preferred
            stockholder will receive a distribution upon liquidation based upon
            the net proceeds from the sale of the entity's assets, to an
            investment in an ongoing fully-integrated real estate company, which
            has a portfolio of properties that may be changed from time to time
            and conducts real estate investment banking operations, in which the
            equity owners are expected to recover the investment from the sale
            of their FSP common stock, which is currently illiquid, and not from
            liquidating distributions; and

      o     FSP Corp. will have substantial flexibility to raise equity capital,
            meaning that investors in FSP Corp. may be subject to dilution.

A comparison of the rights of stockholders of the target REITs and FSP Corp. may
be found in the section of the Consent Solicitation/Prospectus entitled
"Comparison of Stockholder Rights." In addition, selected pro forma consolidated
financial data may be found in the section of the Consent
Solicitation/Prospectus entitled "Selected Pro Forma Consolidated Data" and
selected comparative per share data may be found in the section of the Consent
Solicitation/Prospectus entitled "Comparative Per Share Data."

Tax Consequences of the Mergers

      The mergers are intended to qualify as reorganizations within the meaning
of Section 368(a) of the Internal Revenue Code of 1986, as amended. If the
mergers qualify as reorganizations, there will be no United States federal
income tax consequences to Addison Circle preferred stockholders as a result of
the mergers. The material United States federal income tax considerations
related to the mergers are described in detail in the section of the Consent
Solicitation/Prospectus entitled "Material United States Federal Income Tax
Considerations."

Fairness of the Mergers

      The Board of Directors of Addison Circle believes that the terms of the
merger agreement, when considered as a whole, are fair to the Addison Circle
preferred stockholders and the merger consideration offered in exchange for the
preferred stock of Addison Circle constitutes fair consideration for the
interests of the Addison Circle preferred stockholders. The following provides a
summary of the factors upon which the Addison Circle board based its conclusions
as to the fairness of the mergers and the merger consideration to the Addison
Circle preferred stockholders. Such factors are described in detail in the
section of the Consent Solicitation/Prospectus entitled "Fairness of the
Mergers." The Addison Circle board did not find it practicable to, and did not
attempt to, quantify or otherwise assign relative weight to these factors in
reaching their respective determination.


                                       -4-
<PAGE>

      o     The Addison Circle board compared the potential benefits and
            detriments of the mergers with the potential benefits and detriments
            of several alternatives to the mergers, including continuation of
            Addison Circle, liquidation of Addison Circle and support of
            secondary markets for the Addison Circle stock. Based on these
            comparisons, the Addison Circle board believes the mergers are more
            attractive than other alternatives.

      o     The special committee of the Addison Circle board, consisting of
            Messrs. R. Scott MacPhee and William W. Gribbell, each a member of
            the Addison Circle board and an executive vice president of FSP
            Corp., engaged A.G. Edwards & Sons, Inc. to deliver a fairness
            opinion to the Addison Circle board. On August 11, 2004, A.G.
            Edwards delivered a written opinion to the Addison Circle board to
            the effect that the merger consideration was fair, from a financial
            point of view, to the Addison Circle preferred stockholders. The
            fairness opinion is attached to the Consent Solicitation/Prospectus
            as Appendix C.

      o     The Addison Circle board determined after consultation with A.G.
            Edwards, the financial advisor to Addison Circle and its board, that
            the value of the FSP common stock to be distributed as merger
            consideration to the Addison Circle preferred stockholders
            represented greater value than, or a premium above, the sum of the
            value of the real estate (as determined by an appraisal) and cash
            held by Addison Circle.

      o     The Addison Circle board determined after consultation with A.G.
            Edwards that the value of the FSP common stock to be distributed as
            merger consideration to the Addison Circle preferred stockholders
            was greater than the value that was likely to be realized upon the
            continuation of Addison Circle.

      o     Each target board obtained independent third-party appraisals of the
            real property owned by it, and the Addison Circle board considered
            these appraisals in negotiating the merger consideration.

      o     The Addison Circle board considered historical financial information
            concerning the real estate properties owned by FSP Corp. and the
            target REITs and the amount of cash held by FSP Corp. and each of
            the target REITs.

      o     Addison Circle will have the right to declare dividends consistent
            with past practice in respect of the quarters or partial quarters
            preceding the effective date of the mergers. The combined company
            will have the obligation to pay any such dividends that have been
            declared but not paid as of the effective date.

      o     Certain merger expenses are considered individual expenses to be
            paid by the party incurring the expenses. The costs of A.G.
            Edwards's engagement and the fees of the target REITs' outside
            counsel and accountants will be apportioned among the target REITs
            based on the relative merger consideration received by each target
            REIT's stockholders, and each appraisal will be paid by the target
            REIT owning the property that is the subject of the appraisal. All
            other expenses, including consulting, legal, accounting and
            administrative, will be paid by FSP Corp.


                                       -5-
<PAGE>

      o     The members of the target boards have conflicts of interest in
            connection with the mergers. Each target board established a special
            committee consisting of Messrs. MacPhee and Gribbell, the only
            members of the target boards who are not also members of the FSP
            board. Messrs. MacPhee and Gribbell serve as executive vice
            presidents of FSP Corp. The special committees engaged A.G. Edwards
            to advise them in evaluating and negotiating the terms of the
            mergers, including the merger consideration, and to deliver a
            fairness opinion to each target board. No fees or other compensation
            will be payable to the members of the target boards (or the special
            committees) or to FSP Corp. or its affiliates in connection with the
            mergers.

Determination and Allocation of Merger Consideration

      The merger consideration was determined through arms-length negotiations
between the special committees of the target boards and FSP Corp. Each special
committee relied on advice from its financial advisor, A.G. Edwards, in its
negotiations with FSP Corp. Each special committee also considered the assets
and liabilities of its target REIT, the multiples of cash available for
distribution commonly used in valuing REITs and the limited liquidity of FSP
common stock. Each special committee was also made aware that FSP Corp. intends
to file an application to list the FSP common stock on the American Stock
Exchange. There can be no assurance that FSP Corp. will file such application,
or, in the event it does, that the American Stock Exchange will approve the
application or that a meaningful trading market will develop for the FSP common
stock. In concluding that the merger consideration is fair, the Montague board
relied in part on the recommendation of its special committee, the fairness
opinion delivered by A.G. Edwards for Montague and the appraisal it received for
the property held by Montague.

      In allocating the approximately $192,841,463 of merger consideration among
the target REITs, FSP Corp.'s management considered the appraised values of each
target REIT, the cash flow projected for each target REIT, the cash reserves
held by each target REIT, and the current market conditions for real estate
acquisitions in the various locations of the target REITs. The special
committees, management of FSP Corp., and A.G. Edwards held a telephonic meeting
on July 29, 2004 to discuss the allocation of the merger consideration,
including the allocation of the premiums to be paid by FSP Corp. for each target
REIT. During that call, after reaffirming with all the parties that the stock
price of $17.70 per share of FSP common stock was the negotiated price per share
to be paid as merger consideration, FSP Corp. stated that it was willing to make
an offer to each of the target REITs based, in part, on FSP Corp.'s specific
knowledge of the target REITs' properties which it had gained from the operation
of such properties by FSP Property Management, a wholly owned subsidiary of the
FSP Corp., prior to and following the syndication of the target REITs. FSP Corp.
then suggested a separate value for each target REIT based on its knowledge of
the real properties held by each target REIT, including among other things, the
tenants, the operating costs, current market conditions, FSP Corp.'s view of
future market rents, the likelihood of lease renewals, the costs of turnover,
and FSP Corp.'s experience with acquisitions for similar properties in the same
or similar markets. The negotiations between the parties resulted in agreement
on merger consideration for Addison Circle, Collins Crossing and Royal Ridge
that produced a premium, based on a value of $17.70 per share of FSP common
stock, to the sum of the appraised value of real estate and adjusted cash
balances that ranged from 17.9% to 20.0%. With respect to Montague, FSP Corp.
noted that Montague's property is leased to a single tenant through December 31,
2006 at a rate that is currently significantly above market. FSP Corp. further


                                       -6-
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noted that the appraised value of Montague's real estate was $20,000,000.
Montague's special committee noted that Montague's stockholders were receiving
significant current cash yields as a result of the above-mentioned lease and
that, in the absence of a significant premium to appraised value, those
stockholders might not be inclined to approve a merger. These negotiations
resulted in merger consideration for Montague that produced a premium, based on
the value of $17.70 per share of FSP common stock, of 51.6%.

      As a result of these negotiations, the merger agreement provides for the
Addison Circle preferred stockholders to receive merger consideration valued at
$66,965,414. A summary of certain information considered in the determination of
the value of Addison Circle by the Addison Circle special committee and board
for purposes of the merger consideration follows:

--------------------------------------------------------------------------------
Appraised value of real estate held by Addison Circle                $54,500,000
--------------------------------------------------------------------------------
Dollar amount of any mortgages or liabilities to which                None
appraised real estate held by Addison Circle is subject
--------------------------------------------------------------------------------
Cash held by Addison Circle as of June 30, 2004                      $5,611,989
--------------------------------------------------------------------------------
Other assets held by Addison Circle                                  None
--------------------------------------------------------------------------------
Other liabilities of Addison Circle                                  None
--------------------------------------------------------------------------------
Value assigned to Addison Circle                                     $66,965,414
--------------------------------------------------------------------------------
Value assigned to Addison Circle per share of Addison                $105,292
Circle, of which there are 636 outstanding
--------------------------------------------------------------------------------
Shares of stock in FSP Corp. to be issued as merger                  3,783,354
consideration to Addison Circle preferred stockholders
--------------------------------------------------------------------------------
Percentage of FSP Corp., post-mergers, which the shares              6.25%
of stock in FSP Corp. issued as merger consideration represent
--------------------------------------------------------------------------------
Value assigned to the holdings of FSP Corp. in Addison Circle        None
--------------------------------------------------------------------------------

Compensation Paid By Addison Circle to FSP Corp. and its Affiliates

--------------------------------------------------------------------------------
Compensation paid and cash distributions made from                   $40,207
January 1, 2004 to June 30, 2004
--------------------------------------------------------------------------------
Compensation paid and cash distributions made from                   $79,000
January 1, 2003 to December 31, 2003
--------------------------------------------------------------------------------
Compensation paid and cash distributions made from                   $9,837,870
January 1, 2002 to December 31, 2002
--------------------------------------------------------------------------------
Compensation paid and cash distributions made from                   N/A*
January 1, 2001 to December 31, 2001
--------------------------------------------------------------------------------
*N/A indicates a time period prior to the syndication of Addison Circle.


                                      -7-
<PAGE>

      The compensation, including fees, paid to FSP Corp. and its affiliates
consists primarily of payments made in connection with the original syndication
of interests in Addison Circle, and thereafter of asset management fees. If the
mergers had been reflected prior to such period, Addison Circle would have been
a wholly-owned subsidiary of FSP Corp. and no compensation would have been paid.
The executive officers of FSP Corp. receive compensation from FSP Corp. as set
forth in the section of the Consent Solicitation/Prospectus entitled "Management
- Management Compensation."

Cash Distributions Made to Addison Circle Preferred Stockholders

--------------------------------------------------------------------------------
Cash distributions made from January 1, 2004 to June 30, 2004        $2,552,904
--------------------------------------------------------------------------------
Cash distributions made from January 1, 2003 to December 31, 2003    $4,628,947
--------------------------------------------------------------------------------
Cash distributions made from January 1, 2002 to December 31, 2002    N/A*
--------------------------------------------------------------------------------
Cash distributions made from January 1, 2001 to December 31, 2001    N/A*
--------------------------------------------------------------------------------
Cash distributions made from January 1, 2000 to December 31, 2000    N/A*
--------------------------------------------------------------------------------
Cash distributions made from January 1, 1999 to December 31, 1999    N/A*
--------------------------------------------------------------------------------
*N/A indicates a time period prior to the syndication of Addison Circle.

         You should note that, for the period beginning July 1, 2003 and ending
June 30, 2004 quarterly, non-special cash distributions for each share of
Addison Circle preferred stock totaled $8,078. For that same period, FSP Corp.
paid quarterly, non-special dividends totaling $1.24 per share of FSP common
stock. Each share of Addison Circle preferred stock will receive 5,948.67 shares
of FSP common stock upon consummation of the merger. Thus, on a pro forma basis,
you would have received quarterly, non-special dividends totaling $7,376.35 for
the same period if you had held the number of shares of FSP common stock which
you will receive in exchange for one share of Addison Circle preferred stock, or
approximately 91% of the aggregate amount of quarterly, non-special cash
distributions you did receive as an Addison Circle stockholder

         Selected financial information concerning Addison Circle may be found
in the section of the Consent Solicitation/Prospectus entitled "Selected
Financial Information of FSP Addison Circle Corp." Selected pro forma
consolidated financial data may be found in the section of the Consent
Solicitation/Prospectus entitled "Selected Pro Forma Consolidated Data." Such
information should be read in conjunction with the financial statements of FSP
Corp. and the target REITs and related notes thereto included elsewhere in the
Consent Solicitation/ Prospectus or incorporated therein by reference.


                                      -8-

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