Joaquin Phoenix says he regrets his infamous interview with David Letterman, in which he remained in character for the entire, awkward conversation.

The actor was promoting the mockumentary 'I'm Still Here' when he delivered one of the strangest interviews ever recorded for late night television.

Joaquin Phoenix memorably appeared on 'The Late Show' to speak with David Letterman in 2009 while in character for a 2010 mockumentary he and Casey Affleck made

Joaquin Phoenix deeply regrets his infamous David Letterman interview. The “Joker” actor, 50, appeared” Tuesday and looked back on the infamous exchange he had with Letterman, 78, in the same NYC studio over 15 years ago.

Joaquin Phoenix made his first appearance in 15 years on CBS' "The Late Show" Tuesday night and expressed "regret" over his infamous stunt interview in 2009 with former host David Letterman. After being welcomed to the late-night show by Letterman successor Stephen Colbert,

J oker star Joaquin Phoenix recently returned to The Late Show after a whopping 15 years — but something else also happened: he apologized for his infamous David Letterman interview from 2009 that took place on the show before Letterman turned the reins over to Stephen Colbert.

Joaquin Phoenix was the guest of honor on “The Late Show With Stephen Colbert” on Tuesday night, marking his first appearance on the late-night staple since his infamous 2009 interview with Dave Letterman and subsequent on-air apology the next year.

On Tuesday night, the star said that he originally did the pre-interview in character and “I realized that it was just a little silly, 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.’”

Joaquin Phoenix made an appearance on The Late Show with Stephen Colbert on Tuesday, July 15, where he addressed his notorious 2009 interview with David Letterman. During that infamous appearance, Phoenix stayed in character throughout what turned into an awkwardly cringe-worthy conversation.