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Joy Behar got a HUGE scoop today.

On Behar’s HLN show, airing tonight, Mackenzie Phillips reversed what she had said in her book, “High on Arrival,” about having consensual sex with her father, John Phillips of the Mamas and the Papas group.

As you may recall, Phillips claimed in September that, as she faded in and out of consciousness on a drug-fueled night before her wedding to Jeff Sessler, she and her dad had sex, and then afterwards continued for years sleeping together in what she described as a “consensual” sexual relationship.

Now she changed her story, and Behar got the exclusive.

“I’d like to reframe my word, ‘consensual,’” Phillips told Behar.

She explained, “As I was writing the book, I thought, this word, it kept sitting wrong with me, but I used it for lack of a better word, and since then I’ve been schooled by thousands of incest survivors all across the world that there really is no such thing as consensual incest due to the inherent power a parent has over a child… So, I wouldn’t necessarily call it a consensual relationship at this time.”

A source tells Gossip Cop Behar had no idea Phillips would reverse herself on air, but was “excited she got the scoop.”

And a big scoop it is.

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UPDATE – 10:18PM

“I had sex with my own father.”

Mackenzie Phillips will reveal tomorrow on Oprah that her father, Mamas and Papas founder John Phillips, raped her, Gossip Cop has learned. The interview coincides with the release of her memoir, “High on Arrival.” Already it’s been revealed in promos for tomorrow’s program that her father introduced the “One Day at a Time” star to drugs. She recalls, “My father shot me up for the first time.” She also discusses Mick Jagger‘s attempt to seduce her and other long-held secrets.

But the most stunning revelation is that John had sex with a drugged-out 19-year-old Mackenzie as she faded in and out of consciousness on the eve of her wedding to Jeff Sessler in 1979. According to a leaked copy of the book, when she later confronted him about it, she said, “We have to talk about how you raped me,” to which he responded, “You mean when we made love?” The two had a long-term incestuous relationship, the memoir reveals.

Earlier this afternoon Oprah tweeted, “Interviewed One Day at a Time’s Mackenzie Phillips. Thought I’d heard it all … beyond shocking! We’re airing it Wednesday.”

We contacted Harpo Productions, and they did not get back to us. We also exchanged a series of e-mails with Simon & Schuster, the memoir’s publisher, explaining that we had heard the book’s big secret was that Mackenzie and John Phillips had a long-term sexual relationship. We have now confirmed it.