Mackenzie Phillips

Chynna Phillips appeared on The Oprah Winfrey Show Friday to support her half-sister, Mackenzie Phillips, who said on Wednesday's show that she had an incestuous relationship with their father.

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Chynna previously said in a statement that she believed her sister's account of events. "Who is going to go out of their way to say, 'Yeah, I had sex with Dad'?" she asked.

"I'm very proud of my sister," Chynna told Winfrey on the show. (Though Mackenzie also appeared during the hour, it was only via satellite.) "Am I exceedingly joyful that my family secret, that I've told maybe my therapist, my husband and my very best friend in the world, [is now public]? It's a platform for everybody to know. It's very upsetting," she said.

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Chynna, who now records as one-half of a Christian pop duo called Chynna & Vaughan (with Vaughan Penn), said that she and Mackenzie are not polar opposites. "If I had one piece of advice for my sister, it would be to get the Lord on board, because you're going to need it," she said with a laugh.

For her part, Mackenzie said that while her family's various statements of equivocation have been "heartbreaking," she has been overwhelmed by the public response.

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In addition to receiving more than 150 letters, the online response has been significant. "I had no idea there were this many incest survivors on Facebook," she told Winfrey.