Chynna Phillips, daughter of John and his Mamas & the Papas muse Michelle Phillips, says that she believes her half-sister's story, which she says she first heard in 1997.
"She said, 'I don't know why, but I just really felt the need to call you and tell you something that I think you need to know,'" the singer told Us Weekly. "And she went on to tell me that she had had an incestuous relationship with our dad for about 10 years."
"Somebody could have dropped a piano on my head and I probably wouldn't have felt it," Chynna said. "But I knew it was true. I mean, who in their right mind would make such a claim if it wasn't true?"
"Was he actually raping her? I don't know," she added. "Do I believe that they had an incestuous relationship and that it went on for 10 years? Yes."
John's third wife, Genevieve Waite, mother of Bijou Phillips and Mackenzie's stepmom during the time when the abuse allegedly started, says that her late ex-husband battled his share of demons—but being an amoral father wasn't one of them.
"John was a good man who had the disease of alcoholism and drug addiction," Waite said in a statement that Winfrey read on the air today. "He was incapable, no matter how drunk or drugged he was, of having such a relationship with his own child."
Michelle Phillips, who was married to John for eight years, until 1970, also can't believe that the pioneering singer-songwriter she knew could have done such a thing—and that Mackenzie told her it was joke after first mentioning it in 1997.
"She told me, then she called me back and said, 'You know I'm joking,' " Michelle told the Hollywood Reporter's Showbiz411 blog. "I said it wasn't funny. Mackenzie said, 'I guess we have different senses of humor.'
"John was a bad parent, and a drug addict. But [expletive] his daughter? If she thinks it's true, why isn't she with a good psychiatrist on a couch? I think it's unconscionable that Oprah would let her do her show. I have every reason to believe it's untrue. Oprah should be more judicious about who she has on her show."
"Mackenzie has a lot of mental illness," Michelle continued. "She's had a needle stuck up her arm for 35 years. She was arrested for heroin and coke just recently. She did Celebrity Rehab and now she writes a book. The whole thing is timed...Mackenzie is jealous of her siblings, who have accomplished a lot and did not become drug addicts."
But that "needle stuck up her arm" was also supposedly supplied by Mackenzie's father.
"My father shot me up," she told Oprah, describing how John supplied her with pills, taught her how to roll joints and injected her with cocaine.
"What you've been taught is what you know, and that was kind of like it for me," she said. "I didn't have very good role models."
And ultimately, their sexual relationship became consensual, in a twisted sort of way.
"It's sort of the Stockholm Syndrome, where you begin to love your captor," Mackenzie said. "And I felt great love for my father."
"It was like grasping at smoke," she said of her constant battle for his attention. "Add to that deep, visceral yearning for a connection, cover it with heroin, cocaine, alcohol, marijuana, barbiturates—everything you can think of."
But despite the seemingly unbearable circumstances she allegedly lived under for nearly a decade, Mackenzie insists that she does not hate her father, who died in 2001 of heart disease.
"My father was not a bad man," she said. "He was kind of a testament to what drugs and alcohol—in huge quantities—can do to a person's priorities, their motives.
"I don't hate him. I understand that he was a very tortured man, and he sort of passed that torture down to me."
When Oprah brought up that other members of his family were concerned about the effect Mackenzie's book will have on John's memory, she said that hers wasn't the first story of incest in the world to be swept under the table.
"In the finding redemption and freedom for myself, maybe I'm going to be giving a little piece of it to somebody else to hold onto," she said. "Having this type of story, and still being here to tell the tale, tells me that I'm still here for a reason."
"Interesting that they're not concerned about how it might defame me," Mackenzie said. "I'm taking a huge personal risk telling this story, and I have to say that I loved my father. I still do.
"I know for a fact that I am the only daughter that this happened to, and I don't know why he chose me to visit his demons upon."