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David Letterman greets fans outside "Late Show With David Letterman" at the Ed Sullivan Theater on June 21, 2010 in New York City.
Director of "I'm Still Here," Casey Affleck told The New York Times that no one except his agent knew that Phoenix was faking his transformation from Oscar-nominated actor to rapper wanna-be, but The Hollywood Reporter dug up a 2009 Nuvo interview with Letterman's monologue writer that revealed the talk show host was in on the act.
"Dave knew about it and Dave loved it because he could play along. He could do whatever he wanted with it. And he did, and it was great television," said "Late Show" writer Bill Scheft to Nuvo.
During his performance on Letterman, Phoenix in dark sunglasses gave stoic one-word answers and announced he quit acting to pursue his hip hop music.
Letterman famously ended the segment with, “Joaquin, I’m sorry you couldn't be here tonight.”
For two years, Phoenix kept up the actor unhinged-act until Affleck came clean last week about the "documentary" and his brother-in-law. "It's a terrific performance, it's the performance of his career," Affleck told the Times.
Phoenix's performance was so convincing that when Scheft first outted the actor about the Late Show performance, no one believed him.
"I’ve told people that (everyone was in on the joke), and not only don’t people believe me, they tell me that I’m wrong and that (Phoenix) is a schizophrenic and he needs help and he’s going to end up like his brother," said Scheft in the Nuvo interview.
The writer added, "I saw the segment notes. It’s an act. I saw Ben Affleck’s brother taping the whole thing from offstage."
Phoenix will return to the "Late Show" on September 22 to promote his fake documentary "I'm Still Here."