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At nine, she contracted polio and spent three weeks in an isolation unit in Los Angeles, an episode that she said "marked the end of my childhood". At 13, her brother Michael died in a plane crash. When she was 17, her father died of a heart attack — his final act was to telephone his beloved daughter, who was deliberately ignoring his calls.

Yet, as her mother once professed, there was nothing fragile about Farrow — nor was there anything conventional. She possesses an extraordinary magnetism, which goes some way to explaining the complex path her life has taken.

In her early teens, Farrow sought work on the stage, where she met Salvador Dali, who became a close friend. The two could be found eating butterflies in the Terrace Room at the St Regis Hotel in New York. Liza Minnelli was also a friend; Farrow is said to have been the first to convince Minnelli to crop her hair, after Farrow did the same during an historic episode of Peyton Place, the US sitcom in which she starred, in 1966.

It was here that Farrow forged her role in the public eye; her portrayal of the waiflike Allison MacKenzie turned her into a national icon. Michael Thornton, the writer and biographer, who met Farrow during this time, recalls that she was "very intelligent, tremendously attractive and underrated. She was neither one sex nor the other. She was androgynous. She looked like a denizen of another planet. And she was very young — not mentally, but to look at."

Indeed, Farrow was only 19 when, shortly after, she wooed Frank Sinatra, then 48, when the pair crossed paths on a television set. Sinatra flew Farrow on his private jet to Palm Springs for the weekend and a year later they were married. The unlikely pairing didn't go down well: the couple became the butt of jokes by the comedian Jackie Mason (who stopped after three bullets were fired through his hotel room door), while others mocked Sinatra's latest choice of wife. "I remember his ex-wife Ava Gardner snorting with laughter because of Mia's masculine haircut and saying: 'I always knew he would end up with a boy,'" recalls Thornton. In 1968, Farrow's career took off when she was asked to play the lead in the Roman Polanski horror film Rosemary's Baby. It marked the end of her marriage to Sinatra — he served her divorce papers on the set.

Gaby Wood, the head of books at The Telegraph, who interviewed Farrow seven years ago, says: "I spoke to Polanski about her and he said that he imagined casting someone less frail as Rosemary, but that she turned out to be very tough personally — except when served divorce papers by Sinatra, then she crumbled."

As Farrow's movie career went from strength to strength — she won praise for her portrayal of Daisy Buchanan in The Great Gatsby in 1974 — she escaped the mêlée in an ashram in India, where she meditated with The Beatles. On her return, she met André Previn, the German-Austrian pianist, whom she married in 1971.

It was with Previn that Farrow started her large family: in 1973 and 1976, they adopted three orphans from Vietnam — Lark Song, Summer Daisy Song and Soon-Yi — and had three children of their own – twins Matthew and Sascha, and Fletcher. The couple divorced in 1979 and a year later, Farrow started dating Woody Allen, with whom she adopted two more children, Moses and Dylan. Ronan (christened Satchel) was born in 1987.

It is on her seemingly insatiable need to have children that many of the criticisms of Farrow are based — but those who know her insist she is incredibly maternal. "Mia was a mother figure in the family. She tended to be in charge," said Maria Roach, her childhood friend. "With her family she's tried to achieve a Norman Rockwell experience, with her kids around her all the time. Deep down, we all just wanted to be normal."

Others support this perception of Farrow. "Mia's family is very unusual," said Audrey Sieger, who tutored Farrow's children for more than a decade and described her as "warm, loving, sincere. At any time in these 12 years she has been able to tell me in detail about every one of her kids. They have not been raised by nannies." Gaby Wood adds: "It's representative of one of the most striking things about her: her commitment."

Commitment was not a word that could be applied to Farrow's 12-year relationship with Allen, which was so dysfunctional that the pair lived on opposite sides of New York's Central Park. On the surface, their life together seemed impossibly glamorous; but privately, Farrow claimed he insulted her, refused to sleep with her and sent her into "genuine meltdown".

The balance was tipped in 1992, when Farrow discovered explicit photographs of her adopted daughter Soon-Yi on the mantelpiece and Allen admitted they had been having an affair (they are now married). Twelve months of paranoia, suicide attempts and hysteria ensued — culminating in Farrow taking Allen to court over claims he had molested their adopted daughter, Dylan. The judge found the evidence inconclusive but rejected Allen's attempt to win custody of their three children.

Despite everything, Farrow told her former nanny, Kristi Groteke: "I honestly loved him." Yet Ms Groteke has said there was more to her employer than met the eye: "Scratch the surface of Mia's naivety and bewilderment, and you get a woman who knows what's happening."

Farrow once sent Allen a Valentine's Day card, featuring a photograph of her with the children, with a toothpick stuck in each person's chest. "This is how many hearts you've broken in this family," she wrote. Some have suggested her revelation about Ronan's paternity is the ultimate act of revenge.

Farrow, who adopted six more children between 1992 and 1995, remained in touch with Sinatra until his death in 1998 — during the Allen saga, he offered to send Mafia associates to break Allen's legs. It would be, says Michael Thornton, "entirely unsurprising" if Ronan were Sinatra's son. "I am sure it could have happened any time, even after she was with Woody Allen."

Recently, Farrow has thrown herself into humanitarian work, becoming a goodwill ambassador for Unicef in 2000 and working as an advocate for refugees in Sudan. In 2008, Time magazine voted her one of the world's most influential people.

Her public appearances have been rare: in 2005 she testified on behalf of Polanski in his libel case against Vanity Fair, and in 2010 appeared at The Hague, giving evidence in the war crimes trial of Charles Taylor, the former Liberian president. Tragedy, too, has afflicted her later life: her two additional daughters, Tam and Lark have both died. "Life," she once said, "is about losing everything, gracefully." Alone, in her remote hideaway, Farrow remains, as ever, graceful. Yet the knotted web of her life has yet to be fully untangled.

In her autobiography, What Falls Away, published in 1997, she wrote of the past: "We've put all that behind us now. It's all just part of a strange history." History it may be — but it is, once again, rearing its strange head.