AceShowbiz -

Joaquin Phoenix metaphorically and literally came clean to "Late Show with David Letterman" on Wednesday, September 22 night. The actor apologized to David Letterman for his bizarre behavior last year when attending the talk show with sunglasses on and a bubblegum chewing in his mouth.

Recently, director Casey Affleck admitted to public that the 2009 appearance was a hoax for Phoenix documentary "I'm Still Here". Letterman was allegedly in knowledge of the situation but he denied it during last night's interview. "Was there a script that you and I were working with?" he asked Phoenix, who responded with, "No."

Phoenix made an apology to Letterman, saying "I think that you've interviewed many, many people and I assumed that you would know the difference between a character and a real person. I hope I didn't offend you in any way." Letterman responded, "Oh, no. Oh, no, no, no. I'm telling you, it was so much fun. It was batting practice, you know what I mean? Every one of them was a dinger."

But Letterman did admit that he was tricked. "I've been to see your movies, I've always liked you. I recognize you as a powerful talent - that Johnny Cash thing, you were tremendous in that. And then a year and a half ago, you come out and, honestly, it's like you slipped and hit your head in the tub," he recalled.

"And I knew immediately when you sat down, something ain't right, because if you're really the way you appeared to be, you don't go out. You know what I mean? People don't let guys like you out if you're really like that. You don't go out."

"I'm Still Here" follows the time Phoenix gives up his acting career to become a rap superstar. It was premiered at 67th Venice International Film Festival earlier this month and hit limited theaters days after.

Clip of Phoenix's appearance on "Letterman":