For Ronan, who wakes each day to see a young Frank Sinatra staring back at him in the mirror, it can hardly have been a shock.
And to Manhattan cognoscenti who have long whispered it, Farrow's confession to Vanity Fair magazine confirmed what has been regarded as one of Hollywood's greatest secret love stories."She never stopped loving him," says Sinatra biographer Darwin Porter. It was a love affair that continued even after their divorce and they remained close till the end.
But she left Allen amid scandal, claiming the director was having a sexual relationship with adopted teenage daughter Soon-Yi - he later married her - and was molesting seven-year-old adopted daughter Dylan, an accusation Allen vehemently denied.
Two years later he served her divorce papers on the set of the Roman Polanski film for which she earned a Golden Globe nomination in 1968.
Frank and Mia stayed close, however, even when she was married to the composer-conductor André Previn, whom she divorced in 1979, after having three sons and adopting three at-risk Asian daughters.
They share the same prominent cheekbones, the same turn of nose, full lips, broad forehead, strong chin and, oh, those famous lady-killing blue eyes.
And according to one female conquest of the young New York lawyer with movie-idol looks: "He inherited one of his father's famous attributes - and it wasn't his singing voice."Mia Farrow, now 68, this week admitted that her 25-year-old son Ronan from her 12-year relationship with Woody Allen may have been fathered by Frank Sinatra.
"I am almost in daily touch with the family," she said as a fragile Sinatra lay bedridden after a heart attack in 1997.
Farrow even offered to take over caring for her former husband to permit Barbara a break from being his primary care-giver - and allowing Farrow some prized time alone with her long-time love, who died of bladder cancer and heart disease the following year."Mia was devastated and heartbroken broken when he died," says Porter."She remained close to Sinatra's family even after his death."Moments before Sinatra's funeral at the Church of the Good Shepherd in Beverly Hills, close family gathered in a small anteroom.
Daughter Tina Sinatra recalls that along with brother Frank Jr and sister Nancy: "I was really surprised to see Mia, accompanied by her son [Ronan].
My sister had invited the people closest to us and to dad."And Ronan remains close to the Sinatra family to this day."Tina Sinatra is not very accepting of Ronan but Nancy is fond of him," says Porter.
"I'm told Ronan has no contact with Woody Allen," says Porter.