The guessing game is over. Joaquin Phoenix did not grow a beard and subsequently lose his mind two years ago. It was for a movie.

As we predicted.

The director of "I'm Still Here," Ben Affleck's little brother Casey Affleck, comes clean in a New York Times interview about his new mockumentary.

Yup, we said mock. Not doc.

And Phoenix's strange appearance on "Letterman" in February 2009, just a few months after he "retired" from acting to become a rapper? Also a fake. Even worse: Letterman, who handled it like a pro, wasn't in on the joke.

SODAHEAD SLIDESHOW: See some of the biggest hoaxes of all time.

"It's a terrific performance, it's the performance of his career," Affleck told the Times of Phoenix's two-year portrayal of himself, on-screen and off-, as an aspiring rap star on the brink of ruin.

Critics apparently disagree, delivering crushing reviews that are a far cry from the praise 35-year-old Phoenix received for his Oscar-nominated performances in "Gladiator" and "Walk the Line."

But Affleck, like any good prankster, is defensive about his project.

"I never intended to trick anybody," Affleck told the Times. "The idea of a quote, hoax, unquote, never entered my mind."

Well, Casey, it entered ours -- we saw it coming a mile away. But we can't say the same thing about 2009's "balloon boy" fake-out, which we totally fell for.