Casey Affleck has revealed his new movie about brother-in-law Joaquin Phoenix's efforts to quit acting and become a rapper is one big hoax.
Affleck and Phoenix fooled fans and the media last year as the star announced he was turning his back on Hollywood and then grew a bushy beard and started acting strangely on a series of chat shows, and at appearances.
The madcap scenes were shot by Affleck for his newly-released "I'm Still Here" documentary.
And during recent interviews at both the Venice and Toronto Film Festivals, Affleck insisted the documentary was for real - and his pal and subject really was trying to make it as a rapper.
But in a New York Times article on Thursday, the actor/director confessed the film was an experiment that perhaps went too far.
He said, "I never intended to trick anybody. The idea of a 'hoax' never entered my mind."
But Affleck admitted Phoenix played his part brilliantly - even risking ridicule for a mumbling appearance on chat show host David Letterman's late-night program last year.
He added, "It's a terrific performance, it's the performance of his career."