# EDGAR Filing Document

**Accession Number:** 0002091865
**File Stem:** 0001104659-25-108622
**Filing Date:** 2025-11
**Character Count:** 8612
**Document Hash:** 8d89a66cadd3afe0e0c9d5177641128e
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001104659-25-108622.hdr.sgml**: 20251107

**ACCESSION NUMBER**: 0001104659-25-108622

**CONFORMED SUBMISSION TYPE**: 3

**PUBLIC DOCUMENT COUNT**: 1

**CONFORMED PERIOD OF REPORT**: 20251028

**FILED AS OF DATE**: 20251107

**DATE AS OF CHANGE**: 20251107

**REPORTING-OWNER**: 

**OWNER DATA:**
- **COMPANY CONFORMED NAME:** Irish Simon
- **CENTRAL INDEX KEY:** 0002091865

**ORGANIZATION NAME:**

**FILING VALUES:**
- **FORM TYPE:** 3
- **SEC ACT:** 1934 Act
- **SEC FILE NUMBER:** 001-42252
- **FILM NUMBER:** 251463896

**MAIL ADDRESS:**
- **STREET 1:** 2730 W. TYVOLA ROAD, SUITE 100
- **CITY:** CHARLOTTE
- **STATE:** NC
- **ZIP:** 28210
**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

### 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>Irish Simon<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>[X] Officer (give title below)   [ ] Other (specify below)<br>_Chief Executive Officer_ | **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") | 2295934<sup>(1)</sup> | D |  |
| Common Stock | 2818520<sup>(1)</sup> | I | Through LLC |
| Common Stock | 52255<sup>(1)</sup> | I | Through Defined Benefit Plan |

---

## 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> | 2038-06-16 | Common Stock | 24140 | $2.0133 | D |  |
| Stock Option (Right to Buy) | <sup>(2)</sup> | 2031-01-24 | Common Stock | 107288 | $2.2370 | D |  |
| Stock Option (Right to Buy) | <sup>(2)</sup> | 2029-12-31 | Common Stock | 178812 | 0.2013<sup>(7)</sup> | D |  |
| Stock Option (Right to Buy) | <sup>(2)</sup> | 2034-12-31 | Common Stock | 2279850 | 0.2013<sup>(7)</sup> | D |  |
| Stock Option (Right to Buy) | <sup>(2)</sup> | 2028-12-31 | Common Stock | 178812 | 0.2013<sup>(7)</sup> | D |  |
| Stock Option (Right to Buy) | <sup>(2)</sup> | 2034-12-31 | Common Stock | 2172563 | 0.2013<sup>(7)</sup> | D |  |
| Stock Option (Right to Buy) | 2023-05-19<sup>(3)</sup> | 2032-05-19 | Common Stock | 98347 | $2.2370 | D |  |
| Stock Option (Right to Buy) | <sup>(2)</sup> | 2043-01-01 | Common Stock | 21905 | $2.2370 | D |  |
| Stock Option (Right to Buy) | <sup>(2)</sup> | 2044-01-01 | Common Stock | 26286 | $2.2370 | D |  |
| Stock Option (Right to Buy) | <sup>(2)</sup> | 2045-01-01 | Common Stock | 4381 | $2.2370 | D |  |
| Stock Option (Right to Buy) | 2024-04-01<sup>(3)</sup> | 2043-04-01 | Common Stock | 89406 | $2.2370 | D |  |
| Stock Option (Right to Buy) | 2024-07-14<sup>(3)</sup> | 2033-07-14 | Common Stock | 178812 | $2.2370 | D |  |
| Restricted Stock Units | 2026-10-21<sup>(4)</sup> | 2035-10-21 | Common Stock | 1023160 | <sup>(4)</sup> | D |  |
| Warrants (Right to Buy) | <sup>(5)</sup> | 2028-07-31 | Common Stock | 44703 | $2.2370 | D |  |
| Warrants (Right to Buy) | <sup>(5)</sup> | 2028-07-31 | Common Stock | 89406 | $2.2370 | I | Through Defined Benefit Plan |
| Contingent Value Right | <sup>(6)</sup> | <sup>(6)</sup> | Common Stock | <sup>(6)</sup> | <sup>(6)</sup> | D |  |
| Contingent Value Right | <sup>(6)</sup> | <sup>(6)</sup> | Common Stock | <sup>(6)</sup> | <sup>(6)</sup> | I | Through Defined Benefit Plan |

---

### 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 and accelerated vesting in certain events.

(4) Each restricted stock unit represents a contingent right to acquire one share of Common Stock. The restricted stock units vest in one-half increments on each of the first and second anniversaries of the grant date, subject to Mr. Irish's continued employment through each applicable vesting date and accelerated vesting in certain events.

(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.

**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.**