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Mackenzie Phillips and John Phillips: Incest and Drugs Bombshell

Photo: MacKenzie Phillips and her father John Phillips of "The Mamas and The Papas" on the John Davidson Show on March 5, 1981.

NEW YORK (CBS/AP) A horrifying, almost unbelievable revelation has come out from Mackenzie Phillips, daughter of legendary musician John Phillips.

Read more of "High on Arrival" here.>

The 49-year-old former child star, best known as Julie on the sitcom "One Day at a Time," sat down with Oprah Winfrey to reveal a family secret she's kept hidden for 31 years.

In a preview of her book "High on Arrival," on, she says she had an incestuous relationship with her father, John Phillips of the Mamas and Papas.

Because she was often blasted and blacked out on drugs, Phillips says the first time she was aware of having sex with her father was in 1979 when she was 19. It was the night before she was to get married to a member of the Rolling Stones entourage, Jeff Sessler.

She says her father showed up, determined to stop the wedding. She says she and her father "had tons of pills." She passed out on his bed and woke to find herself having sex with him. She says after that night, the sex became consensual.

The interview is scheduled to air Today, Sept. 23, the same day Phillips' memoir hits shelves.

Read more of "High on Arrival" here.>

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