The Affair star's relative Alexander Wilson was an agent for British intelligence service MI6 and a prolific spy novelist, but 10 years ago she discovered he was also a bigamist who started four families.

Ruth reveals she found out the dark family secret in a memoir written by her grandmother, who was his third wife, and it emerged he had managed to keep his other lives under wraps until his death in 1963.

The actress is now working on developing a TV show based on the bizarre story and hopes to play her late grandmother in the miniseries, according to The Los Angeles Times.

Ruth describes her grandfather as "slightly psychopathic" but she is convinced she inherited her love of acting from him.

"He was acting his whole life," she explains. "Suddenly, this whole strand of my life made sense to me."