Joaquin Phoenix deeply regrets his infamous David Letterman interview.

The “Joker” actor, 50, made an appearance on “The Late Show with Stephen Colbert” Tuesday, reminiscing about the notorious encounter he had with Letterman, 78, in the same NYC studio over 15 years ago.

During that period, Phoenix was promoting his 2010 mockumentary “I’m Still Here,” which depicted his retirement from acting to pursue a career as a hip hop artist. While on Letterman’s show, Phoenix adopted his spoof persona and behaved oddly.

“When I came on this show with Dave, I initially did the pre-interview in character and realized that it was just a little silly,” Phoenix recounted to Colbert, 61.

“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,’” the actor stated.

“So that was the kind of intention,” Phoenix added. “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.”

The Oscar winner went on to call the interview “horrible” and “uncomfortable.”

“I regret it, I’ll never do it again,” he shared. “I’m so sorry.”

“I don’t know if he’s watching,” Colbert joked to Phoenix about Letterman, as Phoenix offered a direct apology to the former “Late Show” host.

“He might be and I just need to say, I’m sorry,” Phoenix said.

Colbert told Phoenix he watched the 2009 interview live and called it “great TV.”

Phoenix, joking about his return to the Ed Sullivan Theater, said to Colbert: “I imagine they did a major exorcism after I left.”

The talk show host then pointed out that Phoenix “got what you wanted” from his infamous sit-down with Letterman.

“It was strange because in some ways, it was a success,” the “Walk the Line” star said, “and it was also just one of the worst nights of my life.”

Phoenix previously apologized to Letterman when he returned to “The Late Show” in 2010.

“I hope I didn’t offend you in any way,” Phoenix said. “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.”

But Letterman wasn’t insulted, saying to Phoenix, “I’m telling you, it was so fun.”