With his bright blue eyes and roguish good looks, Ronan Farrow has never much looked like his father, Woody Allen.
He does, however, bear an uncanny resemblance to Frank Sinatra, the first husband of his mother, Mia Farrow.
Now the actress says there may be a very good reason for this: he could be the son of Ol' Blue Eyes himself.
Responding to years of speculation, Farrow told Vanity Fair that her 25-year-old son was "possibly" fathered by Sinatra, from whom she said she "never really split up" after their divorce in 1968.
Sinatra's daughter, Nancy, confirmed that Ronan Farrow was treated as a member of her family. "He is a big part of us, and we are blessed to have him in our lives," she said.
Making light of the disclosures, Ronan Farrow wrote on Twitter: "Listen, we're all possibly Frank Sinatra's son."
His mother married Sinatra, who was 29 years older, in Las Vegas in 1966. However he demanded a divorce two years later while she was filming the thriller Rosemary's Baby.
Farrow went on to have a nine-year marriage to Andre Previn, the pianist and composer, before embarking on a 12-year relationship with Allen, while also starring in his films, in the 1980s.
They never married and their relationship ended in notoriously acrimonious circumstances when Allen had an affair with Soon-Yi Previn, one of Farrow and Previn's adopted daughters. The Farrows have never forgiven Allen, 77, who married Previn, now 42, in 1997 and has two adopted daughters with her.
Ronan Farrow, a Yale University graduate, human rights activist and former youth adviser to Hillary Clinton, has repeatedly criticised Allen in recent years. He has described Allen's actions as "a moral transgression".
Named Satchel Ronan O'Sullivan Farrow when he was born in 1987, Farrow was presumed to be the sole biological child of Allen and Farrow. The couple also adopted two children. In all, Farrow has four biological children and nine adopted children. Two other adopted children have died.