Terrestrial Energy (HONDU) adds UHY LLP auditor consent to S-4 amendment

Rhea-AI Filing Summary

Terrestrial Energy Inc. filed a Post-Effective Amendment No. 1 to its Form S-4 to furnish a consent from UHY LLP relating to the auditor's report for the financial statements for the years ended December 31, 2025 and December 31, 2024. The amendment is exhibit-only and updates Exhibit 23.1; the proxy statement/prospectus and the remainder of Part II remain unchanged.

Key Figures

Registration Number: 333-288735 Original File Number: 333-291796 EIN: 98-1785406 +3 more

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Registration Number 333-288735 Post-Effective Amendment No. 1 to Form S-4

Original File Number 333-291796 Registration Statement initially filed July 17, 2025

EIN 98-1785406 Issuer tax identification number stated on cover

Exhibit Exhibit 23.1 Consent of UHY LLP filed herewith

Financial statement years Years ended December 31, 2025 and December 31, 2024 Audited financial statements referenced in consent

Amendment/Signature Date March 30, 2026 Date signatures were executed

Key Terms

Post-Effective Amendment, Form S-4, Consent of UHY LLP, Prospectus Supplement No. 2

4 terms

Post-Effective Amendment regulatory

"This Post-Effective Amendment No. 1 to the Registration Statement on Form S-4"

A post-effective amendment is an official update to a securities registration document filed after that document has become effective with regulators; it corrects, adds or replaces information about the securities, the company, or an offering. Investors care because it keeps the legal record current and can change what is being sold or the rights attached to shares — like getting a revised product manual after a launch that may affect value or use.

Form S-4 regulatory

"Amendment to the Registration Statement on Form S-4 of Terrestrial Energy Inc."

A Form S-4 is a legal document that companies file with the government to announce and explain a major business move, such as a merger or acquisition. It provides detailed information to help investors understand how the deal might affect the company's value and future prospects, similar to a detailed blueprint that clarifies the impact of a significant change.

Consent of UHY LLP regulatory

"filed as Exhibit 23.1, Consent of UHY LLP with respect to its report dated March 30, 2026"

Prospectus Supplement No. 2 regulatory

"included in the Prospectus Supplement No. 2 dated March 30, 2026"

As filed with the U.S. Securities and Exchange Commission on March 30, 2026

Registration No. 333-288735

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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

POST-EFFECTIVE AMENDMENT NO.1

TO

FORM S-4 REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

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TERRESTRIAL ENERGY INC.

(Exact name of registrant as specified in its charter)

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Delaware	​ ​ ​	3443	​ ​ ​	98-1785406
(State or other jurisdiction of incorporation or organization)		(Primary Standard Industrial Classification Code Number)		(I.R.S. Employer Identification Number)

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2730 W. Tyvola Road, Suite 100

Charlotte, NC 28217

(646) 687-8212

(Address, including zip code, and telephone number, including area code, of registrant’s principal executive offices)

Simon Irish

Chief Executive Officer

2730 W. Tyvola Road, Suite 100

Charlotte, NC 28217

(646) 687-8212

(Name, address, including zip code, and telephone number, including area code, of agent for service)

Copies to:

Sean Jones

Coleman Wombwell

K&L Gates LLP

300 South Tryon Street

Suite 1000

Charlotte, NC 28202

(704) 331-7406

Approximate date of commencement of proposed sale to the public: As soon as practicable after (i) this registration statement is declared effective and (ii) upon completion of the applicable transactions described in the enclosed proxy statement/prospectus.

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If the securities being registered on this Form are being offered in connection with the formation of a holding company and there is compliance with General Instruction G, check the following box: ☐

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If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering: ☐

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If this Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering: ☒ 333-288735

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Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act:

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Large accelerated filer	☐	Accelerated filer	☐
Non-accelerated filer	☒	Smaller reporting company	☒
		Emerging growth company	☒

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If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act: ☐

If applicable, place an ☒ in the box to designate the appropriate rule provision relied upon in conducting this transaction:

Exchange Act Rule 13e-4(i) (Cross-Border Issuer Tender Offer) ☐

Exchange Act Rule 14d-1(d) (Cross-Border Third-Party Tender Offer) ☐

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This Post-Effective Amendment No. 1 to the Registration Statement Shall become effective immediately upon filing with the Securities and Exchange Commission in accordance with Rule 462(d) under the Securities Act.

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EXPLANATORY NOTE

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This Post-Effective Amendment No. 1 (this “Amendment”) to the Registration Statement on Form S-4 of Terrestrial Energy Inc. (File No. 333-291796), initially filed on July 17, 2025, and declared effective by the Securities and Exchange Commission on September 26, 2025 (the “Registration Statement”), is being filed as an exhibit-only filing solely to file a consent of UHY LLP with respect to its report dated March 30, 2026 relating to the financial statements of Terrestrial Energy Inc. for the years ended December 31, 2025 and December 31, 2024 contained in the Company’s Annual Report on Form 10-K for the year ended December 31, 2025 and included in the Prospectus Supplement No. 2 dated March 30, 2026 filed pursuant to Rule 424(b)(3), filed herewith as Exhibit 23.1 (the “Consent”). Accordingly, this Amendment consists only of the facing page, this explanatory note, Item 21 of Part II of the Registration Statement, the signature pages to the Registration Statement, and the Consent. The proxy statement/prospectus and the balance of Part II of the Registration Statement are unchanged hereby and have been omitted.

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Part II

INFORMATION NOT REQUIRED IN PROSPECTUS

Item 21. Exhibits and Financial Statement Schedules.

(a)Exhibits.

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									​	​
Number	​ ​ ​	Description	​ ​ ​	Form	​ ​ ​	Exhibit	​ ​ ​	Date Filed with the SEC	​ ​ ​	File Number
23.1	*	Consent of UHY LLP	​	​	​	​	​	​	​	​

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* Filed herewith

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SIGNATURES

Pursuant to the requirements of the U.S. Securities Act of 1933, as amended, the registrant has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Charlotte, State of North Carolina, on March 30, 2026.

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TERRESTRIAL ENERGY INC.		​
By:	/s/ Simon Irish	​
Name:	Simon Irish	​
Title:	Chief Executive Officer	​

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Pursuant to the requirements of the Securities Act, this registration statement has been signed by the following persons in the capacities and on the dates indicated below.

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Signature	​ ​ ​	Title	​ ​ ​	Date
​	​	​	​	​
/s/ Simon Irish	​	Chief Executive Officer and Director	​	March 30, 2026
Simon Irish	​	(Principal Executive Officer)	​	​
​	​	​	​	​
/s/ Brian Thrasher	​	Chief Financial Officer	​	March 30, 2026
Brian Thrasher	​	(Principal Financial and Accounting Officer)	​	​
​	​	​	​	​
*	​	Chairman of the Board of Directors	​	March 30, 2026
Frederick Buckman	​	​	​	​
​	​	​	​	​
*	​	Director	​	March 30, 2026
Shawn Matthews	​	​	​	​
​	​	​	​	​
*	​	Director	​	March 30, 2026
Hugh MacDiarmid	​	​	​	​
​	​	​	​	​
*	​	Director	​	March 30, 2026
David Hill	​	​	​	​
​	​	​	​	​
*	​	Director	​	March 30 2026
Charles Pardee	​	​	​	​
​	​	​	​	​
*	​	Director	​	March 30, 2026
Robert W. Jones	​	​	​	​
​	​	​	​	​
*	​	Director	​	March 30, 2026
William Johnson	​	​	​	​
​	​	​	​	​
*	​	Chief Technology Officer and Director	​	March 30, 2026
David LeBlanc	​	​	​	​

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By:	/s/ Simon Irish	​
Name:	Simon Irish	​
	Attorney-in-fact	​

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FAQ

What did Terrestrial Energy (HONDU) file in this Post-Effective Amendment?

They filed a Post-Effective Amendment No. 1 adding an auditor consent from UHY LLP. The filing attaches Exhibit 23.1 and states the proxy statement/prospectus and remaining Part II are unchanged.

Does the amendment change the registered securities or offering terms?

No. The amendment is exhibit-only and does not change the registered securities or offering terms. It only files the UHY LLP consent related to audited financial statements.

Which financial periods are covered by the auditor consent?

The consent relates to audited financial statements for the years ended December 31, 2025 and December 31, 2024. Those statements were included in the Annual Report on Form 10-K and Prospectus Supplement No. 2.

When did Terrestrial Energy submit this amendment?

The signature block shows the amendment was signed and filed on March 30, 2026. The filing indicates the registration statement was initially declared effective on September 26, 2025.

Where is the auditor consent filed in the registration statement?

The auditor consent is filed as Exhibit 23.1 to the Post-Effective Amendment No. 1. The amendment lists Item 21 (Exhibits) and notes Exhibit 23.1 is "Filed herewith."