Mackenzie Phillips' step-mother says she doesn't believe the U.S. actress's claims she had a long-term incestuous relationship with her father.

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The former "One Day at a Time" star, who has battled drug addiction for years, wrote in her new memoir, "High on Arrival," that she and her father, the late Mamas and the Papas musician John Phillips, had sex on many occasions from the time she was 19 to 29.

Usmagazine.com quoted Mackenzie, 49, as saying on "The Oprah Winfrey Show" this week that the improper relationship ended when she had an abortion because she didn't know who had impregnated her.

The actress said her father paid for the procedure and "and I never let him touch me again."

However, the actress's step-mother, Michelle Phillips, told The Hollywood Reporter she doesn't believe the allegations.

"She told me, then she called me back and said, 'You know I'm joking,'" Michelle said. "I said it wasn't funny. Mackenzie said, 'I guess we have different senses of humor.'"

Michelle also criticized Winfrey for inviting Mackenzie on her chat show to discuss her book.

"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's step-mother told The Hollywood Reporter. "Mackenzie has a lot of mental illness. 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."