The One Thing Mackenzie Phillips Wasn’t Prepared For

At just 16 years old, Mackenzie Phillips was one of the most popular television stars in America. She was the boy-crazy teenage sister of Valerie Bertinelli on the megahit One Day at a Time. She was also the real-life daughter of John Phillips, leader of the legendary band The Mamas and the Papas.

Growing up in the world of sex, drugs and rock 'n' roll, teenage Mackenzie lived a life fueled by drug abuse. After decades of addiction, arrests and rehab, Mackenzie came on The Oprah Winfrey Show in 2009 with a jaw-dropping family secret: Between the ages of 18 and 29, she had a sexual relationship with her father.

"It became a consensual relationship over time," Mackenzie said during her appearance, "and I know I can't be the only one this has happened to."

Mackenzie said the relationship finally came to an end when she became pregnant. "I did not know who the father was," Mackenzie said. "The implications, the reality, of that...I had an abortion. And I never let him touch me again."

Oprah recently sat down again with Mackenzie to ask what it was like after the show aired on TV. Watch the above video to find out why she was in "terror" on the show. Plus, the one thing she wasn't prepared for.