Initial Statement of Beneficial Ownership (Form 3)

FORM 3

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940

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(Print or Type Responses)

1. Name and Address of Reporting Person * LeBlanc David Michael 2. Date of Event Requiring Statement (Month/Day/Year) 10/28/2025 3. Issuer Name and Ticker or Trading Symbol Terrestrial Energy Inc. /DE/ [IMSR] (Last) (First) (Middle) 2730 W. TYVOLA ROAD, SUITE 100 4. Relationship of Reporting Person(s) to Issuer (Check all applicable) __X__ Director _____ 10% Owner __X__ Officer (give title below) _____ Other (specify below) Chief Technology Officer 5. If Amendment, Date Original Filed (Month/Day/Year) (Street) CHARLOTTE, NC 28217 6. Individual or Joint/Group Filing (Check Applicable Line) _X_ Form filed by One Reporting Person ___ Form filed by More than One Reporting Person (City) (State) (Zip) Table I - Non-Derivative Securities Beneficially Owned

1.Title of Security (Instr. 4) 2. Amount of Securities Beneficially Owned (Instr. 4) 3. Ownership Form: Direct (D) or Indirect (I) (Instr. 5) 4. Nature of Indirect Beneficial Ownership (Instr. 5) Common Stock, par value $0.0001 per share ("Common Stock") 5,981(1) D Common Stock 13,731(1) I Through Entity

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Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)

1. Title of Derivative Security (Instr. 4)	2. Date Exercisable and Expiration Date (Month/Day/Year)		3. Title and Amount of Securities Underlying Derivative Security (Instr. 4)		4. Conversion or Exercise Price of Derivative Security	5. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 5)	6. Nature of Indirect Beneficial Ownership (Instr. 5)
	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Stock Option (Right to Buy)	(2)	06/16/2038	Common Stock	17,792	$2.0133	D
Stock Option (Right to Buy)	(2)	01/01/2043	Common Stock	53,197	$2.237	D
Stock Option (Right to Buy)	(2)	01/01/2044	Common Stock	63,836	$2.237	D
Stock Option (Right to Buy)	(2)	01/01/2045	Common Stock	10,640	$2.237	D
Exchangeable Shares	(3)	(3)	Common Stock	11,175,778	(3)	D
Warrants (Right to Buy)	(4)	07/31/2028	Common Stock	17,882	$2.237	D
Warrants (Right to Buy)	(4)	07/31/2028	Common Stock	41,575	$2.237	I	Through Entity
Contingent Value Right	(5)	(5)	Common Stock	(5)	(5)	D
Contingent Value Right	(5)	(5)	Common Stock	(5)	(5)	I	Through Entity

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
LeBlanc David Michael 2730 W. TYVOLA ROAD, SUITE 100 CHARLOTTE, NC 28217	X		Chief Technology Officer

Signatures

/s/ Steven M. Millsap, pursuant to Power of Attorney		11/07/2025
**Signature of Reporting Person		Date

Explanation of Responses:

*	If the form is filed by more than one reporting person, see Instruction 5(b)(v).
**	Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
(1)	Upon closing of the business combination (the "Business Combination") between Terrestrial Energy Inc., a Delaware corporation formerly known as HCM II Acquisition Corp. ("New Terrestrial"), and Terrestrial Energy Development Inc., a Delaware corporation formerly known as Terrestrial Energy Inc. ("Legacy Terrestrial"), 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 Business Combination Agreement, dated as of March 26, 2025, by and among HCM II Acquisition Corp., HCM II Merger Sub Inc. and Legacy Terrestrial.
(2)	Consists of options granted pursuant to the Legacy Terrestrial Second Amended and Restated 2024 Stock Option Plan. The options are currently exercisable.
(3)	Represents exchangeable shares in the capital of Terrestrial Energy Canada (Exchange) Inc., an indirect wholly-owned subsidiary of New Terrestrial, which are exchangeable for Common Stock of New Terrestrial, subject to adjustment. The exchangeable shares have no expiration date.
(4)	Consists of Legacy Terrestrial warrants to purchase common stock that are currently exercisable.
(5)	Consists of contingent value right issued upon conversion of Legacy Terrestrial convertible notes in connection with the Business Combination. Each contingent value right entitles the holder to receive additional shares of Common Stock in the event that the volume weighed average price of the Common Stock for the twenty (20) trading days beginning on the trading day immediately following expiration of the lock-up period contemplated by the applicable Legacy Terrestrial convertible note is less than seventy-five percent (75%) of the redemption price ($7.905).
Remarks: Exhibit List - Exhibit 24.1 - Power of Attorney

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