Spacey's remarks came in a tweet posted on Sunday night after "Star Trek: Discovery” star Anthony Rapp alleged that Spacey climbed on top of him in bed when he was just 14 years old.
"I have a lot of respect and admiration for Anthony Rapp as an actor. I'm beyond horrified to hear this story," Spacey said. "I honestly do not remember the encounter ... But if I did behave then as he describes, I owe him the sincerest apology for what would have been deeply inappropriate drunken behavior."
Spacey went on to say that the situation "encouraged me to address other things about my life."
"As those closest to me know," Spacey continued in his tweet. "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."
Rapp, now 46, accused Spacey of trying to seduce him while attending a party back in 1986.
"He picked me up like a groom picks up the bride over the threshold. But I don't, like, squirm away initially, because I'm like, 'What's going on?' And then he lays down on top of me," Rapp said in a BuzzFeed article published Sunday.
"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," Rapp added.
Rapp reiterated his comments in three tweets early Monday, shortly after Spacey released his statement, and said he would not comment any further.
"I came forward with my story, standing on the shoulders of the many courageous women and men who have been speaking out to shine a light and hopefully make a difference, as they have done for me," Rapp wrote Monday.
He continued, "Everything I wanted to say about my experience is in that article, and I have no further comment about it at this time."
Beau Willimon, creator of the hit Netflix show "House of Cards" in which Spacey stars, reacted to the news Monday morning in a statement posted to Twitter.
"Anthony Rapp's story is deeply troubling," he began. "During the time I worked with Kevin Spacey on 'House of Cards' I neither witnessed nor was aware of any inappropriate behavior on set or off. That said, I take reports of such behavior seriously, and this is no exception. I feel for Mr. Rapp and I support his courage."
ABC News reached out to Netflix in wake of the accusations, but didn't immediately hear back.