<SEC-DOCUMENT>0001213900-25-104331.txt : 20251030
<SEC-HEADER>0001213900-25-104331.hdr.sgml : 20251030
<ACCEPTANCE-DATETIME>20251030203115
ACCESSION NUMBER:		0001213900-25-104331
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20251028
FILED AS OF DATE:		20251030
DATE AS OF CHANGE:		20251030

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Matthews Shawn
		CENTRAL INDEX KEY:			0001855118
		ORGANIZATION NAME:           	

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-42252
		FILM NUMBER:		251437670

	MAIL ADDRESS:	
		STREET 1:		100 FIRST STAMFORD PLACE, SUITE 330
		CITY:			STAMFORD
		STATE:			CT
		ZIP:			06902

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			HCM Investor Holdings II, LLC
		CENTRAL INDEX KEY:			0002019800
		ORGANIZATION NAME:           	
		STATE OF INCORPORATION:			E9
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-42252
		FILM NUMBER:		251437669

	BUSINESS ADDRESS:	
		STREET 1:		100 FIRST STAMFORD PLACE
		CITY:			STAMFORD
		STATE:			CT
		ZIP:			06902
		BUSINESS PHONE:		203-930-2200

	MAIL ADDRESS:	
		STREET 1:		100 FIRST STAMFORD PLACE
		CITY:			STAMFORD
		STATE:			CT
		ZIP:			06902

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			Terrestrial Energy Inc. /DE/
		CENTRAL INDEX KEY:			0002019804
		STANDARD INDUSTRIAL CLASSIFICATION:	FABRICATED PLATE WORK (BOILER SHOPS) [3443]
		ORGANIZATION NAME:           	04 Manufacturing
		EIN:				981785406
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		2730 W. TYVOLA ROAD, SUITE 100
		CITY:			CHARLOTTE
		STATE:			NC
		ZIP:			28217
		BUSINESS PHONE:		203-930-2200

	MAIL ADDRESS:	
		STREET 1:		2730 W. TYVOLA ROAD, SUITE 100
		CITY:			CHARLOTTE
		STATE:			NC
		ZIP:			28217

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	HCM II Acquisition Corp.
		DATE OF NAME CHANGE:	20240415
</SEC-HEADER>
<DOCUMENT>
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<SEQUENCE>1
<FILENAME>ownership.xml
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<ownershipDocument>

    <schemaVersion>X0508</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2025-10-28</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0002019804</issuerCik>
        <issuerName>Terrestrial Energy Inc. /DE/</issuerName>
        <issuerTradingSymbol>IMSR</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001855118</rptOwnerCik>
            <rptOwnerName>Matthews Shawn</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O HCM INVESTOR HOLDINGS II, LLC</rptOwnerStreet1>
            <rptOwnerStreet2>100 FIRST STAMFORD PLACE, SUITE 330</rptOwnerStreet2>
            <rptOwnerCity>STAMFORD</rptOwnerCity>
            <rptOwnerState>CT</rptOwnerState>
            <rptOwnerZipCode>06902</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0002019800</rptOwnerCik>
            <rptOwnerName>HCM Investor Holdings II, LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O HCM INVESTOR HOLDINGS II, LLC</rptOwnerStreet1>
            <rptOwnerStreet2>100 FIRST STAMFORD PLACE, SUITE 330</rptOwnerStreet2>
            <rptOwnerCity>STAMFORD</rptOwnerCity>
            <rptOwnerState>CT</rptOwnerState>
            <rptOwnerZipCode>06902</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>1</isOther>
            <officerTitle></officerTitle>
            <otherText>Former 10% owner</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>0</aff10b5One>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock, par value $0.0001 per share</value>
            </securityTitle>
            <transactionDate>
                <value>2025-10-28</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>5675000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>5675000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Footnote</value>
                    <footnoteId id="F2"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock, par value $0.0001 per share</value>
            </securityTitle>
            <transactionDate>
                <value>2025-10-28</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
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                <equitySwapInvolved>0</equitySwapInvolved>
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            <transactionAmounts>
                <transactionShares>
                    <value>533514</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F3"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>533514</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Warrants</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>11.50</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2025-10-28</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>4275000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>11.50</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2025-11-27</value>
            </exerciseDate>
            <expirationDate>
                <value>2030-10-28</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock, par value $0.0001 per share</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>4275000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4275000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Footnote</value>
                    <footnoteId id="F2"/>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Warrants</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>11.50</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2025-10-28</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>1267599</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>11.50</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2025-11-27</value>
            </exerciseDate>
            <expirationDate>
                <value>2030-10-28</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock, par value $0.0001 per share</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>1267599</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1267599</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Footnote</value>
                    <footnoteId id="F4"/>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Upon closing of the business combination (the &quot;Business Combination&quot;) between the Issuer (which was formerly known as HCM II Acquisition Corp. or &quot;HCM II&quot;) and Terrestrial Energy Inc. (&quot;Terrestrial&quot;) the reporting person acquired these securities in exchange for the reporting person's securities in Terrestrial pursuant to the terms and conditions of the business combination agreement, dated March 26, 2025 and as amended on October 28, 2025, by and among HCM II, Terrestrial and HCM II Merger Sub Inc. (the &quot;BCA&quot;). The reporting person resigned as an officer of HCM II upon the closing of the Business Combination.</footnote>
        <footnote id="F2">Mr. Matthews is the sole managing member of HCM Investor Holdings II, LLC (the &quot;Sponsor&quot;), which is registered owner of these shares and warrants, and Mr. Matthews holds voting and investment power with respect to shares and warrants held of record by the Sponsor.</footnote>
        <footnote id="F3">Upon closing of the Business Combination, between Terrestrial Energy Inc., a Delaware corporation formerly known as HCM II Acquisition Corp. (&quot;New Terrestrial&quot;), and Terrestrial Energy Development Inc., a Delaware corporation formerly known as Terrestrial Energy Inc. (&quot;Legacy Terrestrial&quot;), the reporting person acquired these securities in exchange for the reporting person's securities in Legacy Terrestrial pursuant to the terms and conditions of the BCA.</footnote>
        <footnote id="F4">Mr. Matthews is the sole managing member of Hondo Holdings LLC, which is registered owner of these warrants, and Mr. Matthews holds voting and investment power with respect to warrants held of record by Hondo Holdings LLC.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Shawn Matthews, by Steven Bishcoff, Attorney-in-Fact</signatureName>
        <signatureDate>2025-10-30</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ HCM Investor Holdings II, LLC, by Steven Bischoff, Attorney-in-Fact</signatureName>
        <signatureDate>2025-10-30</signatureDate>
    </ownerSignature>
</ownershipDocument>
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</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
