The question of paternity has always been a popular parlor game in Hollywood, where a well-kept secret is as rare as a faithful marriage. When the truth inevitably seeps out and targets a child, who picks up the pieces?

Allegra Huston knows. In a beautifully written memoir, “Love Child,” she chronicles her earliest memories of unfathomable loss, her involuntary transition from a “proper little English girl” to an inconvenient little Hollywood house guest and her ultimate triumph over the pain of deceit.

The name alone evokes Hollywood royalty and should have guaranteed Allegra a fairy tale existence. Her grandfather, Walter Huston, established a brilliant career as a character actor in the early days of film. Her father, the legendary filmmaker and notorious womanizer John Huston, directed such classics as “The Maltese Falcon” and “The African Queen.”

Allegra’s mother, the beautiful Italian-American ballerina Ricki Soma, was 19 when she married John Huston and pregnant with the couple’s son, Tony. Their daughter, Anjelica, who would eventually add another Oscar to the Huston collection, arrived in 1951.

“Dad was a difficult person to be married to, and Mum was the fourth woman to attempt it,” Allegra writes. “He was unfaithful, egocentric, impatient, judgmental, cuttingly sarcastic, and a gambler.”

By the time Allegra was born in 1964, her beloved Mum and Huston were leading separate lives: Ricki and the three children lived in upper-middle-class London while Huston resided at his magnificent Irish estate, St. Clarens.

“Love Child” begins with Allegra reaching into “the treacherous depths of my memory” to relive the night she was told her mother had died. She remembers sitting on her Mum’s bed with her two siblings, “two darks heads flanking my little blond one. They’re much older than me; eighteen and seventeen. I am four,” and hearing the awful words. “I let out a sound that my sister describes as a banshee wail,” writes Allegra. “It chilled her. I didn’t cry.”

Shortly after her Mum died (Ricki was killed instantly in a car crash while vacationing in Italy), Allegra met a man “with long fingers holding a long brown cigar.” The man was Huston. “This is your father,” a voice told her. Allegra had never even seen him before.

The globe-trotting Huston drew the little girl into his orbit — and to St. Clerans— and the shy, pudgy child forged a tentative bond with this “infrequent visitor.”

After three years in Ireland, Allegra was involuntarily shuttled to Long Island — with no explanation — to live with her mother’s elderly parents. But nothing remained permanent in Allegra’s life and she soon moved across the country to Hollywood and to the home Huston shared with his fifth (and last) wife, Cici.

On the upside, Hollywood allowed Allegra to reconnect with her beautiful, glamorous sister, now a successful actress. She often stayed with “Anjel” at the opulent digs of the bad-boy lover du jour: Jack Nicholson, fun-loving and perpetually buzzed, and, later, the vile-tempered, coke-snorting Ryan O’Neal.

However tenuous her love affairs, Anjelica deeply cared for her little sister and provided much-needed refuge when 12- year old Allegra suffered another body blow to her fragile psyche. Her stepmother, Cici, in the throes of a nasty divorce

from Huston, inexplicably revealed to Allegra a long-held secret: “John isn’t really your father,” she announced. “Your mother went out and found love,” Cici went on. “You were a child of love.”

This time Allegra cried uncontrollably, partly from relief. “It all made sense: meeting Dad when I was too old to meet a father. . . . the constant uncertainty about where I belonged,” she writes.

Allegra’s biological father, renowned British historian and aristocrat John Julius Norwich, had also been married at the time of his passionate love affair with Ricki. After his first awkward visit with Allegra (Cici brought him to Hollywood to meet her) their relationship, and her relationship with his children, gradually evolved into a warm, close bond.

Allegra successfully bridged her loyalties between two families by referring to Norwich as her father. John Huston, who always knew the truth but never spoke of it, would always be her dad.

Why do we care about a little girl on the outermost periphery of celebrity? Because she makes us care—with her words. “Love Child” is written with such emotional restraint that the reader aches to protect her.

And we take comfort knowing that Allegra Huston — living in New Mexico as a writer, editor, mother and lover — eventually pieced together the fragments of Ricki Soma’s legacy.

Love Child:A Memoir of Family Lost and Found By Allegra Huston Simon & Schuster 286 pages, $26.95

The former Carol Jasen was a top-rated Ch. 4 anchor and is a member of the Buffalo Broadcasting Hall of Fame.