Seemingly out of nowhere week, we saw Mackenzie Phillips on Oprah, revealing a long held family secret - that she had a 10-year sexual affair with her father and possibly even became pregnant by him before having an abortion.

Well, we haven't seen the last of the 49-year-old on the daytime talk show. Mackenzie is returning to The Oprah Winfrey Show tomorrow (Friday) afternoon.

Joining her? Half-sister Chynna Phillips, who spoke out this week in support of Mackenzie, who she says confessed the affair to her 11 years after it ended.

Mackenzie will appear via satellite on Friday, while Chynna will be live in the studio. It is not clear if the two will interact or if they'll appear only separately.

Mackenzie Phillips, left, and Chynna Phillips.

On Wednesday's show, Mackenzie confessed her long-running, drug-addled sexual affair with her dad, John Phillips of '60s band The Mamas and the Papas.

She said she became pregnant and didn't know who fathered the child. She had an abortion, which her father paid for, "and I never let him touch me again."

Chynna later revealed her side of her sister's sad and disturbing story, which Mackenzie is making public for the first time in her new memoir, High on Arrival.

In an interview, she said that news of the affair sent her into "a deep, deep sadness and depression for about 10 days. A part of me died when I found out."

It will be interesting to see what transpires on Friday's show.

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