Oscar winner Joaquin Phoenix has finally explained why he appeared in his combative rap persona during his infamous Late Show With David Letterman interview in 2009 as he was promoting his high-concept mockumentary, I’m Still Here.

Phoenix was back on The Late Show Tuesday night, this time with host Stephen Colbert, to promote his new film, Ari Aster’s Eddington, marking the first time the lauded actor, who portrayed the wildly popular Joker in two films over the past decade, has stopped by the Late Show‘s longtime home of the Ed Sullivan Theater in New York since his follow-up apology for the disastrous interview with Letterman.

In his 2009 Letterman appearance and the film, Phoenix plays a version of himself that was giving up a promising acting career to pursue a new one as a rapper.

I’m Still Here was a flop; the interview with Letterman has gone down as one of late-night television’s most awkward, as a bushy-haired-and-scraggly-bearded Phoenix tells Letterman he’s making him feel weird, gives curt “thank you” answers, refuses to answer other questions in any sort of engaging manner and generally makes Letterman’s life hell for eight full minutes. Phoenix explained the story of that night to Colbert this week. 

“When I came on this show with Dave, I originally did the pre-interview in character, and I realized that it was just a little silly,” Phoenix recalled to Colbert. “So I called them back and I said, ‘Listen, this is what I’m doing. I’m coming out here and I’m doing this whole thing. And I just want Dave to like, lacerate me. I just want it to be really dangerous. 

“So that was the kind of intention,” he said. “I just always wanted to get this reaction and see how I would respond to that. So it was beneficial for no one to know, except when needed.”

Phoenix offered his opinion on the resulting television moment, telling Colbert that he finds it to be absolutely “horrible.”

“It was so uncomfortable. I regret it, I’ll never do it again. I’m so sorry,” he said, then contemplating whether Letterman was watching the show that night.  “He might be, and I just need to say, ‘I’m sorry,’” Phoenix said, 

In 2010, the actor returned to The Late Show and did apologize, in a way, to Letterman for the disaster of an interview. 

“I hope I didn’t offend you in any way,” he said back then. “You’ve interviewed many, many people, and I assumed that you would know the difference between a character and a real person, but I apologize.”

As he contemplated this moment, Phoenix told Colbert on Tuesday: “It was strange because in some ways, it was a success, and it was also just one of the worst nights of my life.”