Rumours have swirled about Lord Mountbatten’s ­private life since his assassination in an IRA bomb attack 40 years ago

He was the war hero who led allied efforts in southeast Asia, the statesman who was so admired as last viceroy of India that he was invited to be its first governor-general, and the family man who was Prince Philip’s uncle and a valued mentor to Prince Charles.

But recently uncovered FBI files and new interviews paint the 1st Earl Mountbatten of Burma as a sexually voracious man whose bisexuality became a theme of US intelligence files. The documents came to light during research for a biography of Lord Mountbatten and his wife Edwina by Andrew Lownie, a fellow of the Royal Historical Society and president of the Biographers’ Club.

Since the assassination of Mountbatten in an IRA bomb attack 40 years ago, rumours have