In a candid interview with ABC's Nightline discussing her new memoir, You Have No Idea, the Desperate Housewives star not only talked about that terrible episode in her young life but also dropped another bombshell: She had an abortion in high school.
"Being pregnant is the most frightening thing that happens in your life," said Williams. "I knew in high school that's something that I was not prepared to do or fight or struggle with."
Regarding the day she was molested by an 18-year-old girl on a family trip just a few years before, the singer-actress admitted that she initially contemplated not putting the shocking incident in the book.
"It was definitely a choice, because it didn't need to be [in there]," Williams added. "It happened one night where she told me, 'Come over here'…I didn't know that it was wrong, but I knew that it wasn't right because I wasn't supposed to tell anybody."
That episode, the full realization of which didn't hit her until she was in college, was partly to blame for her rebellious teen years, she said.
"I think I was highly sexualized because I was in fifth grade and I had this experience," remarked the onetime Miss America. "Because it feels good, you're like, OK, well this is supposed to be normal. That's not normal for a 10-year-old to be seduced."
Williams, now 49, was joined in the sit-down by her mom, Helen, who cowrote the memoir and acknowledged being "absolutely stunned" to find out that her daughter had been molested.
"[I] had no idea that that had happened," the elder Williams told Nightline. "But in retrospect, it kind of put into place some of her reactions during her preteen years."
The full interview airs tonight at 11:35 p.m. ET.