UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): August 6, 2020

SIRIUS INTERNATIONAL INSURANCE GROUP, LTD.

(Exact name of registrant as specified in charter)

14 Wesley Street

Hamilton HM 11, Bermuda

(Address of principal executive offices)

(441) 278-3140

(Registrant’s telephone number, including area code)

N/A

(Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

x  Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

¨  Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

¨ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

¨ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act:

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (17 CFR §230.405) or Rule 12b-2 of the Securities Exchange Act of 1934 (17 CFR §240.12b-2). Emerging growth company ¨

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 13(a) of the Exchange Act. ¨

Item 8.01. Other Events.

Joint Press Release

On August 6, 2020, Sirius International Insurance Group, Ltd., a Bermuda exempted company (the “Company”), and Third Point Reinsurance Ltd., a Bermuda exempted company (“TPRE”), issued a joint press release announcing the execution of an Agreement and Plan of Merger (the “Merger Agreement”), by and among the Company, TPRE and Yoga Merger Sub Limited, a Bermuda exempted company and wholly owned subsidiary of TPRE (“Merger Sub”). A copy of the press release is attached as Exhibit 99.1 to this Current Report on Form 8-K and is incorporated herein by reference.

Cautionary Statements Regarding Forward-Looking Information

This Current Report on Form 8-K contains forward-looking statements within the meaning of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934, including statements about the future financial condition, results of operations and operating activities of the Company (together with its subsidiaries, “Sirius Group”). Forward-looking statements are typically identified by words such as “plan,” “believe,” “expect,” “anticipate,” “intend,” “outlook,” “estimate,” “forecast,” “project,” “target,” “continue,” “could,” “may,” “might,” “will,” “possible,” “potential,” “predict,” “should,” “would,” “seeks,” “likely” and other similar words and expressions, but the absence of these words does not mean that a statement is not forward-looking. The forward-looking statements are based on the current expectations of the management of the Company and speak only as of the date of this Current Report on Form 8-K. There can be no assurance that future developments will be those that have been anticipated. These forward-looking statements involve a number of risks, uncertainties or other assumptions that may cause actual results or performance to be materially different from those expressed or implied by these forward-looking statements. The general factors that could cause actual results or performance to be materially different from those expressed or implied include, without limitation, the following:

Should one or more of these risks or uncertainties materialize, or should any of the assumptions made by the management of the Company prove incorrect, actual results may vary in material respects from those projected in these forward-looking statements. Except to the extent required by applicable law or regulation, Sirius Group undertakes no obligation to update these forward-looking statements to reflect events or circumstances after the date of this Current Report on Form 8-K.

Additional Information Regarding the Transaction and Where to Find It

This Current Report on Form 8-K does not constitute an offer to sell or the solicitation of an offer to buy any securities or a solicitation of any vote or approval. This communication is being made in respect of the proposed merger transaction involving the Company, TPRE and a wholly-owned subsidiary of TPRE, among other things. The proposed merger transaction will be submitted to the shareholders of each of the Company and TPRE for their consideration, and TPRE will file a registration statement for the securities to be issued in the proposed merger transaction. In connection therewith, the parties intend to file relevant materials with the SEC, including a definitive joint proxy statement/prospectus, which will be mailed to the shareholders of the Company and the shareholders of TPRE. However, such documents are not currently available. BEFORE MAKING ANY VOTING OR ANY INVESTMENT DECISION, INVESTORS AND SECURITYHOLDERS OF THE COMPANY AND/OR TPRE ARE URGED TO READ THE DEFINITIVE JOINT PROXY STATEMENT/PROSPECTUS REGARDING THE PROPOSED MERGER TRANSACTION AND ANY OTHER RELEVANT DOCUMENTS FILED OR TO BE FILED WITH THE SEC CAREFULLY AND IN THEIR ENTIRETY WHEN THEY BECOME AVAILABLE BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION ABOUT THE PROPOSED MERGER TRANSACTION. Investors and security holders may obtain free copies of the definitive joint proxy statement/prospectus, any amendments or supplements thereto and other documents containing important information about each of the Company and TPRE, once such documents are filed with the SEC, through the website maintained by the SEC at www.sec.gov. Copies of the documents filed with the SEC by the Company will be available free of charge under the “Investor Relations” section of the Company’s website located at http://www.siriusgroup.com or by contacting the Company’s Investor Relations Department at (212) 312-2525 or Investor.Relations@siriusgroup.com. Copies of the documents filed with the SEC by TPRE will be available free of charge under the “Investors” section of TPRE’s website located at http://www.thirdpointre.com or by contacting TPRE’s Investor Relations Department at (441) 542-3333 or investorrelations@thirdpointre.bm.

Participants in the Solicitation

The Company and TPRE, and their respective directors and executive officers, certain other members of their respective management and certain of their respective employees, may be deemed to be participants in the solicitation of proxies in connection with the proposed merger transaction. Information about the directors and executive officers of the Company is set forth in its proxy statement for its 2019 annual general meeting of shareholders, which was filed with the SEC on April 5, 2019, its annual report on Form 10-K for the fiscal year ended December 31, 2019, which was filed with the SEC on March 5, 2020, as amended by Amendment No. 1 to its annual report on Form 10-K filed with the SEC on April 21, 2020, and information about the directors and executive officers of TPRE is set forth in its proxy statement for its 2020 annual general meeting of shareholders, which was filed with the SEC on April 27, 2020, and its annual report on Form 10-K for the fiscal year ended December 31, 2019, which was filed with the SEC on February 28, 2020, each of which can be obtained free of charge from the sources indicated above. Other information regarding the participants in the proxy solicitation and a description of their direct and indirect interests, by security holdings or otherwise, will be contained in the definitive joint proxy statement/prospectus and other relevant materials to be filed with the SEC when they become available.

(d) Exhibits:

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, as amended, the Registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.