<SEC-DOCUMENT>0001213900-25-104333.txt : 20251030
<SEC-HEADER>0001213900-25-104333.hdr.sgml : 20251030
<ACCEPTANCE-DATETIME>20251030203306
ACCESSION NUMBER:		0001213900-25-104333
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:			Brenner Andrew Scott
		CENTRAL INDEX KEY:			0002030321
		ORGANIZATION NAME:           	

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-42252
		FILM NUMBER:		251437672

	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>
<TYPE>4
<SEQUENCE>1
<FILENAME>ownership.xml
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0508</schemaVersion>

    <documentType>4</documentType>

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

    <notSubjectToSection16>1</notSubjectToSection16>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0002030321</rptOwnerCik>
            <rptOwnerName>Brenner Andrew Scott</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 Director</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>25000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>25000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <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, by and among HCM, Terrestrial and HCM II Merger Sub Inc. (the &quot;BCA&quot;). The reporting person resigned as a director of HCM II upon the closing of the Business Combination.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Andrew Brenner, by Steven Bishcoff, Attorney-in-Fact</signatureName>
        <signatureDate>2025-10-30</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
