The Andover Companies, a long-standing mutual insurance group in the Northeast, is among the investors in Mereo Insurance, a Bermuda-based (re)insurance startup chaired by former AIG Executive Chairman and CEO Brian Duperreault.

The Andover Companies closed its investment in Mereo Holdings Limited, parent company of Mereo Insurance, on January 31.

Mereo has secured more than $700 million to fund its new reinsurance operations.

Mereo Insurance has already received a financial strength rating of A- from AM Best and is actively writing business for February reinsurance renewals. The company will focus its diversified portfolio across approximately 25 lines of business, including property, casualty, and specialty insurance and reinsurance.

“Mereo’s seasoned leadership and innovative strategy align with our vision of diversifying into new classes of business and geographic markets. We believe this partnership will drive long-term value and further strengthen our portfolio,” said Chuck DiGrande, president and CEO of The Andover Companies.

Other investors in the startup include alternative asset manager Ares Management Corp. and quantitative trading firm Susquehanna International Group. Mereo has indicated it is accepting further equity commitments until the end of March.

The Andover Companies includes Merrimack Mutual, Cambridge Mutual, and Bay State. They write personal and business insurance in Massachusetts, Maine, New Hampshire, Rhode Island, Connecticut, New York, New Jersey, and Illinois.