OneBeacon Insurance Group, the US unit of Bermuda-based White Mountains Insurance Group Ltd., announced a management shake-up on Friday with chief operating officer Mike Miller being promoted to president and chief executive after the departure ?for personal reasons? of ex-chief executive John Cavoores.

The Boston-based company ? OneBeacon Insurance Group ? recruited Mr. Miller in April from his previous position as co-chief operating officer at rival St. Paul Travelers, White Mountains said in a press statement.

OneBeacon was subpoenaed in recent weeks by Connecticut Attorney General Richard Blumenthal for documents and other information about how the company did business with insurance brokers, White Mountains said in a US Securities and Exchange Commission filing at the time.

Mr. Cavoores? departure follows the company being hit by the sudden departure of one of its board members, Joseph Steinberg, a week ago, for personal reasons. A White Mountains executive, John Gillespie also left the company at the same time.

Mr. Gillespie had been chairman and president of White Mountains Advisors after serving from 2001 to 2003 as managing director of OneBeacon.

Both he and Mr. Steinberg held a stake in a Bermuda-reinsurer Olympus that counts nearly all of its business from White Mountains.

Mr. Steinberg stepped down from the White Mountains board after coming under fire for also sitting on Olympus? board as well as owning stakes in both companies through his chief executive position at conglomerate Leucadia National Corporation.

Mr. Cavoores owned a minority stake in Olympus. And Mr. Gillespie was also a minority shareholder through investment management arrangements by Prospector Partners, a company that White Mountains was an owner of until a split between the two groups was announced last week.

In addition to Mr. Gillespie leaving his job at White Mountains, so did an undisclosed number of White Mountains Advisors equity professionals.

White Mountains maintains a revenue stake in Prospector which is now being run as an autonomous venture by Mr. Gillespie.