# EDGAR Filing Document

**Accession Number:** 0001144845
**File Stem:** 0001104659-25-108628
**Filing Date:** 2025-11
**Character Count:** 11880
**Document Hash:** f0019df33687e9472d056ab650adf2ad
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001104659-25-108628.hdr.sgml**: 20251107

**ACCESSION NUMBER**: 0001104659-25-108628

**CONFORMED SUBMISSION TYPE**: 3

**PUBLIC DOCUMENT COUNT**: 2

**CONFORMED PERIOD OF REPORT**: 20251028

**FILED AS OF DATE**: 20251107

**DATE AS OF CHANGE**: 20251107

**REPORTING-OWNER**: 

**OWNER DATA:**
- **COMPANY CONFORMED NAME:** BUCKMAN FREDERICK W
- **CENTRAL INDEX KEY:** 0001144845

**ORGANIZATION NAME:**

**FILING VALUES:**
- **FORM TYPE:** 3
- **SEC ACT:** 1934 Act
- **SEC FILE NUMBER:** 001-42252
- **FILM NUMBER:** 251463909

**MAIL ADDRESS:**
- **STREET 1:** QUANTA SERVICES, INC.
- **STREET 2:** 1360 POST OAK BLVD., SUITE 2100
- **CITY:** HOUSTON
- **STATE:** TX
- **ZIP:** 77056-3023
**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

## Exhibit 24.1

**Exhibit 24.1**

**POWER OF ATTORNEY**

The undersigned hereby makes, constitutes and appoints each of Simon Irish, Brian Thrasher and Steven Millsap, or any of them acting singly, and with full power of substitution, re-substitution and delegation, the undersigned's true and lawful attorney-in-fact (each of such persons and their substitutes and delegees being referred to herein as the "Attorney-in-Fact"), with full power to act for the undersigned and in the undersigned's name, place and stead, in the undersigned's capacity as an officer, director or stockholder of Terrestrial Energy Inc. (the "Company"), to:

&nbsp;&nbsp;&nbsp;&nbsp;1. Prepare and execute any and all forms, schedules and other documents (including any amendments thereto)
the undersigned is required to file with the Securities and Exchange Commission ("SEC"), or which the Attorney-in-Fact considers
it advisable for the undersigned to file with the SEC, under Section 13 or Section 16 of the Securities Exchange Act of 1934
or any rule or regulation thereunder (the "Exchange Act"), or under Rule 144 under the Securities Act of 1933 ("Rule 144"),
including Forms 3, 4 and 5, Schedules 13D and 13G, and Forms 144 (all such forms, schedules and other documents being referred to herein
as "SEC Filings");

&nbsp;&nbsp;&nbsp;&nbsp;2. Submit and file SEC Filings with the SEC, or cause them to be submitted and filed, utilizing the EDGAR
system;

&nbsp;&nbsp;&nbsp;&nbsp;3. File, submit or otherwise deliver SEC Filings to any securities exchange on which the Company's securities
may be listed or traded; and

&nbsp;&nbsp;&nbsp;&nbsp;4. Obtain, as the undersigned's representative and on the undersigned's behalf, information regarding transactions
in the Company's equity securities from any third party, including the Company and any brokers, dealers, employee benefit plan administrators
and trustees, and the undersigned hereby authorizes any such third party to release any such information to the Attorney-in-Fact.

The undersigned acknowledges that:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;a) This Power of Attorney authorizes, but does not require, the Attorney-in-Fact to act in his or her discretion
on information provided to such Attorney-in-Fact without independent verification of such information;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;b) Any documents prepared or executed by the Attorney-in-Fact on behalf of the undersigned pursuant to this
Power of Attorney will be in such form and will contain such information as the Attorney-in-Fact, in his or her discretion, deems necessary
or desirable;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;c) Neither the Company nor the Attorney-in-Fact assumes any liability for the undersigned's responsibility
to comply with the requirements of Section 13 or Section 16 of the Exchange Act or Rule 144, any liability of the undersigned
for any failure to comply with such requirements, or any liability of the undersigned for disgorgement of profits under Section 16(b) of
the Exchange Act; and

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;d) This Power of Attorney does not relieve the undersigned from responsibility for compliance with the undersigned's
obligations under Section 13 or Section 16 of the Exchange Act, including, without limitation, the reporting requirements under
Section 13 or Section 16 of the Exchange Act.

The undersigned hereby grants to the Attorney-in-Fact full power and authority to do and perform each and every act and thing requisite, necessary or advisable to be done in connection with the foregoing, as fully, to all intents and purposes, as the undersigned might or could do in person, hereby ratifying and confirming all that the Attorney-in-Fact, or his or her substitute or substitutes, shall lawfully do or cause to be done by authority of this Power of Attorney.

This Power of Attorney shall remain in full force and effect until the undersigned is no longer required to file Forms 4 or 5 or Schedules 13D or 13G or Forms 144 with respect to the undersigned's holdings of and transactions in securities of the Company, unless earlier revoked by the undersigned in a signed writing delivered to the Attorney-in-Fact. This Power of Attorney revokes all previous powers of attorney with respect to the subject matter of this Power of Attorney.

IN WITNESS WHEREOF, the undersigned has executed this Power of Attorney as of November 4, 2025.

---

| |
|:---|
| /s/ Frederick W. Buckman Sr. |
| Frederick W. Buckman Sr. |

---

### UNITED STATES SECURITIES AND EXCHANGE COMMISSION
**Washington, D.C. 20549**

## FORM 3

### INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES

[ ] Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

---

| | | |
|:---|:---|:---|
| **1. Name and Address of Reporting Person**<sup>*</sup><br>BUCKMAN FREDERICK W<br><sub>(Last) (First) (Middle)</sub><br>2730 W. TYVOLA ROAD, SUITE 100<br><sub>(Street)</sub><br>CHARLOTTE, NC 28217<br><sub>(City) (State) (Zip)</sub> | **3. Issuer Name and Ticker or Trading Symbol**<br>Terrestrial Energy Inc. /DE/ [ IMSR ] | **5. If Amendment, Date of Original Filed (Month/Day/Year)**<br>  |
| **2. Date of Event Requiring Statement (Month/Day/Year)**<br>2025-10-28 | **4. Relationship of Reporting Person(s) to Issuer**<br>(Check all applicable)<br>[X] Director   [ ] 10% Owner<br>[ ] Officer (give title below)   [ ] Other (specify below)<br>_ _ | **6. Individual or Joint/Group Filing (Check Applicable Line)**<br>[X] Form filed by One Reporting Person<br>[ ] Form filed by More than One Reporting Person |

---

## Table I - Non-Derivative Securities Beneficially Owned

---

|  |  |  |  |
| --- | --- | --- | --- |
| 1. Title of Security | 2. Amount of Securities Beneficially Owned | 3. Ownership Form | 4. Nature of Indirect Beneficial Ownership |
| Common Stock, par value $0.0001 per share ("Common Stock") | 6669<sup>(1)</sup> | D |  |
| Common Stock | 14930<sup>(1)</sup> | I | Through Trust |

---

## Table II - Derivative Securities Beneficially Owned

---

|  |  |  |  |  |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- |
| 1. Title of Derivative Security | 2. Date Exercisable and Expiration Date (Month/Day/Year) | 2. Date Exercisable and Expiration Date (Month/Day/Year) | 3. Title and Amount of Underlying Securities | 3. Title and Amount of Underlying Securities | 4. Conversion or Exercise Price | 5. Ownership Form | 6. Nature of Indirect Beneficial Ownership |
| 1. Title of Derivative Security | Date Exercisable | Expiration Date | Title | Amount or Number of Shares | 4. Conversion or Exercise Price | 5. Ownership Form | 6. Nature of Indirect Beneficial Ownership |
| Stock Option (Right to Buy) | <sup>(2)</sup> | 2036-10-01 | Common Stock | 22352 | 1.4764<sup>(6)</sup> | D |  |
| Stock Option (Right to Buy) | <sup>(2)</sup> | 2037-11-19 | Common Stock | 111758 | $2.0133 | D |  |
| Stock Option (Right to Buy) | 2024-04-01<sup>(3)</sup> | 2043-04-01 | Common Stock | 67055 | $2.2370 | D |  |
| Stock Option (Right to Buy) | 2026-02-03<sup>(3)</sup> | 2045-02-03 | Common Stock | 67055 | $2.2370 | D |  |
| Warrants (Right to Buy) | <sup>(4)</sup> | 2028-07-31 | Common Stock | 22352 | $2.2370 | D |  |
| Warrants (Right to Buy) | <sup>(4)</sup> | 2028-07-31 | Common Stock | 44703 | $2.2370 | I | Through Trust |
| Contingent Value Right | <sup>(5)</sup> | <sup>(5)</sup> | Common Stock | <sup>(5)</sup> | <sup>(5)</sup> | D |  |
| Contingent Value Right | <sup>(5)</sup> | <sup>(5)</sup> | Common Stock | <sup>(5)</sup> | <sup>(5)</sup> | I | Through Trust |

---

### Footnotes:

(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) 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).

(6) Price is expressed in Canadian dollars.

**Remarks:**
Exhibit List - Exhibit 24.1 - Power of Attorney

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

### Remarks:

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 4 (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.**