Actor Anthony Rapp, best known for his role in Star Trek: Discovery, gave an interview to Buzzfeed in which he alleged Kevin Spacey made sexual advances to him when he was a 14-year-old boy.
Spacey, then aged 26, is alleged to have invited Rapp to his New York apartment for a party before picking him up and placing him on his bed when the party had finished.
Rapp, now 46, claims Spacey then climbed on top of him and made sexual advances before he managed to 'wriggle free'.
He told Buzzfeed his "stomach churns" when he sees Spacey on film or television.
He said: "I still to this day can't wrap my head around so many aspects of it. It's just deeply confusing to me.
"He was trying to seduce me. I don't know if I would have used that language. But I was aware that he was trying to get with me sexually.
Within hours of the allegations surfacing, Spacey posted a statement on Twitter apologising to Rapp but saying he could not remember the incident.
He also publicly came out as gay for the first time.
The statement said: "I have a lot of respect and admiration for Anthony Rapp as an actor. I'm beyond horrified to hear his story.
"I honestly do no remember the encounter, it would have been over 30 years ago.
"But if I did behave then as he describes, I owe him the sincerest apology for what would have been deeply inappropriate drunken behaviour, and I am sorry for the feelings he describes having carried with him all these years.
"This story has encouraged me to address other things about my life."
"I know that there are stories out there about me and that some have been fuelled by the fact that I have been so protective of my privacy.
"As those closest to me know, in my life I have had relationships with both men and women. I have loved and had romantic encounters with men throughout my life, and I choose now to live as a gay man.
"I want to deal with this honestly and openly and that starts with examining my own behaviour."