AM Best has placed the credit ratings of Hamilton Re and its subsidiaries under review with developing implications after the resignation of its CEO Brian Duperreault.

Reacting to the rating service’s action, Jonathan Reiss, Hamilton Insurance Group’s chief financial officer, said last night: “Hamilton’s regulators, ratings agencies and other key constituents understand the strength of our organisation and the opportunities that have been announced today.

“AM Best’s decision to put the company ‘under review with developing implications’ is consistent with that collective confidence.”

Mr Duperreault yesterday left the company to become president of American International Group.

In a statement, AM Best said: “The rating action reflects AIG’s tentative agreement to acquire all outstanding shares of Hamilton US Holdings Inc, a wholly owned subsidiary of Hamilton Insurance Group Ltd. for approximately $110 million.”

It said the action also reflected the transfer of Attune ownership from HUSA to Hamilton Insurance Group Ltd, as well as other provisions as outlined in the memorandum of understanding between AIG, Hamilton, and Two Sigma Insurance Quantified.

The rating service said the “under review with developing implications status” reflected the complex nature of the transaction, with potential financial and operational benefits and disadvantages.

The ratings will remain under review pending AM Best’s evaluation of Hamilton’s final revised business plan and full analysis of the transaction, as well as the appointment of a permanent replacement for Mr Duperreault.

AM Best has placed under review with developing implications the financial strength rating of A-, and the long-term issuer credit ratings of “a-” of Hamilton Re, Ltd, Hamilton Specialty Insurance Company and Hamilton Insurance Company.