Selma Blair has shared for the first time that she was sexually assaulted by someone she trusted.

In her new memoir, "Mean Baby," the actress revealed that she was just a teenager when she endured abuse at the hands of one of the deans of Cranbrook boarding school that she attended in Bloomfield Hills, Michigan, according to People.

"I counted on him for everything. I really couldn't believe my good fortune in having such a wonderful mentor and friend. What hurt me from this was that he would make such a mistake. That was it," Blair said of her relationship with the man who broke her trust.

"I thought he was the greatest man I had ever met. Handsome. Tall. So generous. I'm sure you can see where this is all going. But at that time, I couldn't have predicted it. I trusted authority. I was just a teenager," she wrote.

Detailing the traumatic experience in her memoir, the "Cruel Intentions" actress wrote that she was about to go on winter break in her freshman year, so she went into the dean's office to say goodbye and exchange gifts.

"We embraced. It felt too long and too still and too quiet. His hand went to the small of my back, tracing the space just above my tailbone. His lips were on my mouth. Please, I thought. Please don't go under my pants, my dress-code-approved Ralph Lauren khakis into which I'd carefully tucked a plaid shirt Please. You are a grown-up and I love you; please do not put your hand inside my pants. But he did. It was a simple thing. He didn't rape me. He didn't threaten me. But he broke me. Nothing ever happened again, but I never felt safe," she wrote.

selma blair vf oscars 2019
Selma Blair attends the 2019 Vanity Fair Oscar Party hosted by Radhika Jones at Wallis Annenberg Center for the Performing Arts on Feb. 24, 2019 in Beverly Hills, California. Dia Dipasupil/Getty Images

"When I told my mother he had kissed me she took a deep breath. 'You must not tell anybody. He's beloved at that school. And you'll just be a troubled girl . . . I'm sorry.' At the end of my senior year, he came over to congratulate me on winning a writing award. Then he turned to my mother and said, 'You must be so proud.' She just looked at him, stone-faced. Then: 'I know what you did. Stay away from my daughter.' He walked away," Blair added.

"I didn't have the energy or experience or the shame factor or the confidence to deal with any of this. And it affected me so very much. I worked very hard in the book to try and (explain) what it was. It was too disarming for me. I was careful, I never wanted him to be in trouble either."

Looking back on that disturbing moment, Blair said that she doesn't let it impact how she views her romantic future. But, for now, she is happy being a single parent to her 10-year-old son Arthur, whom she shares with her ex, Jason Bleick, a fashion designer.

"I feel much more secure in my life. As long as my son is okay, and I don't have an immediate death sentence or am in immediate peril, then I could probably handle anything," she shared.