Harvey Weinstein attempted to set-up a threesome between himself, Cara Delevingne and another woman, according to the Suicide Squad star.
The bisexual actress reveals she had a scary experience with the disgraced Hollywood executive after he quizzed the Brit over the phone about her sexuality, asking Cara if she had actually had sex with any of the women she had been linked romantically to.
The producer allegedly went on to tell the 25-year-old she would not have a career in Hollywood if she was gay.
Cara subsequently met with Weinstein and a director about a movie role and agreed to stay to chat with the producer after the director left. She claims he began to talk about inappropriate sexual subjects and asked her to go to his room.
She reluctantly agreed after his assistant allegedly told her her car wasn't ready yet, and discovered there was another woman already there.
"I was relieved to find another woman in his room and thought immediately I was safe," she writes in a long post on Instagram. "He asked us to kiss and she began some sort of advances upon his direction (sic). I swiftly got up and asked him if he knew that I could sing. And I began to sing... i thought it would make the situation better... more professional... like an audition... i was so nervous.
"After singing I said again that I had to leave. He walked me to the door and stood in front of it and tried to kiss me on the lips. I stopped him and managed to get out of the room."
The actress appeared in his film Tulip Fever - a part she now admits she feels guilty about taking.
"I still got the part for the film and always thought that he gave it to me because of what happened," she adds. "Since then I felt awful that I did the movie. I felt like I didn't deserve the part. I was so hesitant about speaking out... I didn't want to hurt his family. I felt guilty as if I did something wrong.
"I was also terrified that this sort of thing had happened to so many women I know but no one had said anything because of fear."
And she is now urging all women to speak about their experiences.
"I want women and girls to know that being harassed or abused or raped is NEVER their fault and not talking about it will always cause more damage than speaking the truth," she adds in a separate post. "I am relieved to be able to share this... i (sic) actually feel better and I'm proud of the women who are brave enough to speak... this isn't easy but there are strength in our numbers. As I said, this is only the beginning. In every industry and especially in Hollywood, men abuse their power using fear and get away with it. This must stop. The more we talk about it, the less power we give them."
Weinstein was fired from The Weinstein Company after decades of sexual harassment and abuse allegations were detailed in recent New York Times and New Yorker articles.
He has admitted to inappropriate behaviour, but denies other specific allegations against him.