Brooke Shields's Bombshell of the Day: She Lost Her Virginity to Dean Cain
11/12/2014 AT 03:00 PM EST
All these years later, Brooke Shields still admits she was "the most celebrated virgin of our time" – and she can only laugh about how everyone is still talking about it.
In her new book, There Was a Little Girl, which focuses on her complicated relationship with her mom, the star reveals new details about the obsession with her (nonexistent) sex life and explains how she first slept with her college boyfriend (and future Superman) Dean Cain when she was 22.
"The whole virginity thing happened quite genuinely," says Shields, 49. Back in the late '70s, her mom, Teri, insisted she include a chapter about her virginity in her teen memoir, The Brooke Book.
"I had no problem talking about it because I talked about it with my friends," Shields says. "My mother thought it was important for me to then represent that to kids. I was just honest, and like, 'By the way, I also didn't smoke and I had braces.' These things were not off limits with regard to the public and their knowledge of me so I thought, 'Okay, that'll be a good chapter.' "
When she met Cain at Princeton University, they were "instantly crazy" about each other. They were, she writes, "always holding hands and trying to find ways to be alone and kiss, but poor guy, I made him wait."
Now, she says, "I think it was more tortuous for him because I was used to shutting that part [of me] off." And she was always more focused on her omnipresent mom: "I felt as if she was watching."
After they had sex, Shields became so overwhelmed that she jumped out of their bed.
"I actually kind of tumbled off it and started running," she writes in her memoir. "I was buck naked streaking down the hallway and running like I had just stolen someone's wallet."
Cain ran after her with the comforter and asked her where she was going.
"I didn't know where I began and where my mother ended," writes Shields of her confusion. "And that meant I didn't know how to fit Dean in." (They broke up soon after.)
Shields recently called Cain to let him know she was including the memorable episode in her book.
"He said 'As long as you're happy with it, I'm comfortable with it,' " she says. "There's nothing sordid about it. He's such a good guy and a sweet human being."
Still, she adds, "Of course, I wasn't present emotionally but that's a couple of years more therapy."
Shields can only marvel at the fact that her virginity became such an obsession.
"To this day, we're still talking about it, and my kids were in vitro so, who knows?" she says. "Maybe the jury is still out on that one."
For more of Brooke's bombshells, come back to PEOPLE.com every day at 3 p.m. ET! And for much more of PEOPLE's exclusive excerpt from Brooke Shields's memoir and her revealing interview, pick up a copy of the newest issue, on newsstands Friday