IMSR director’s Form 3 lists shares, options, and exchangeables

Rhea-AI Filing Summary

Terrestrial Energy Inc. (IMSR) filed an initial statement of beneficial ownership for a director effective 10/28/2025.

The reporting person holds 25,946 shares of Common Stock (direct). Derivative holdings include stock options for 447,030 shares at $0.0028 (CAD) expiring 02/01/2036; 670,544 shares at $1.1185 (CAD) expiring 02/01/2036; 111,758 shares at $1.4764 (CAD) expiring 02/06/2037; and smaller grants including 6,035 shares at $2.0133 expiring 06/16/2038. Additional options at $2.237 cover 11,176 (expires 05/19/2042) and 78,231 (expires 04/01/2043), with others expiring through 01/01/2045. Prices noted in CAD.

The filing lists Exchangeable Shares for 558,787 (direct) and 134,109 (indirect) shares, exchangeable into Common Stock with no expiration, and warrants for 78,231 shares at $2.237 expiring 07/31/2028. A contingent value right may deliver additional shares if the 20‑day VWAP after the lock‑up is below 75% of the $7.905 redemption price. Holdings reflect exchanges tied to the Business Combination with Legacy Terrestrial.

SEC 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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1. Name and Address of Reporting Person^*

MacDiarmid John Hugh

(Last) (First) (Middle)

2730 W. TYVOLA ROAD, SUITE 100

(Street)

CHARLOTTE NC 28217

(City) (State) (Zip)

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 ]

4. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

X	Director		10% Owner
	Officer (give title below)		Other (specify below)

5. If Amendment, Date of Original Filed (Month/Day/Year)

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

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")	25,946(1)	D

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: 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)	02/01/2036	Common Stock	447,030	$0.0028(7)	D
Stock Option (Right to Buy)	(2)	02/01/2036	Common Stock	670,544	$1.1185(7)	D
Stock Option (Right to Buy)	(2)	02/06/2037	Common Stock	111,758	$1.4764(7)	D
Stock Option (Right to Buy)	(2)	06/16/2038	Common Stock	6,035	$2.0133	D
Stock Option (Right to Buy)	05/19/2023(3)	05/19/2042	Common Stock	11,176	$2.237	D
Stock Option (Right to Buy)	(2)	01/01/2043	Common Stock	18,776	$2.237	D
Stock Option (Right to Buy)	(2)	01/01/2044	Common Stock	22,531	$2.237	D
Stock Option (Right to Buy)	(2)	01/01/2045	Common Stock	3,756	$2.237	D
Stock Option (Right to Buy)	04/01/2024(3)	04/01/2043	Common Stock	78,231	$2.237	D
Exchangeable Shares	(4)	(4)	Common Stock	558,787	(4)	D
Exchangeable Shares	(4)	(4)	Common Stock	134,109	(4)	I	Through Corporation
Warrants (Right to Buy)	(5)	07/31/2028	Common Stock	78,231	$2.237	D
Contingent Value Right	(6)	(6)	Common Stock	(6)	(6)	D

Explanation of Responses:

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. Consists of options granted pursuant to the Legacy Terrestrial Second Amended and Restated 2024 Stock Option Plan. The options vest in one-third increments on each of the first, second and third anniversaries of the grant date, subject to the reporting person's continued service through each applicable vesting date.

4. 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.

5. Consists of Legacy Terrestrial warrants to purchase common stock that are currently exercisable.

6. 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).

7. Price is expressed in Canadian dollars.

Remarks:

Exhibit List - Exhibit 24.1 - Power of Attorney

	/s/ Steven M. Millsap, pursuant to Power of Attorney	11/07/2025
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* 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).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.

FAQ

What did Terrestrial Energy (IMSR) disclose in this Form 3?

An initial beneficial ownership report for a director, including 25,946 Common Stock (direct) and multiple derivative positions.

How many Common Shares does the reporting person directly own in IMSR?

The filing shows 25,946 shares of Common Stock (direct).

What key stock options were reported for IMSR?

Options include 447,030 at $0.0028 (CAD) expiring 02/01/2036 and 670,544 at $1.1185 (CAD) expiring 02/01/2036, among others.

What are the Exchangeable Shares in the IMSR filing?

They are shares of Terrestrial Energy Canada (Exchange) Inc. exchangeable into IMSR Common Stock: 558,787 (direct) and 134,109 (indirect).

Were any warrants disclosed in the IMSR Form 3?

Yes, warrants for 78,231 shares at $2.237 expiring on 07/31/2028.

What triggers the contingent value right (CVR) mentioned?

It delivers additional shares if the 20‑day VWAP after the lock‑up is below 75% of the $7.905 redemption price.

How were these holdings obtained?

Per the filing, securities were received in exchange for Legacy Terrestrial holdings in connection with the Business Combination.