Russian stunner Irina Shayk found out she will grace the cover of the 2011 Sports Illustrated swimsuit issue on The Late Show with David Letterman Monday, as the show had its’ traditional unveiling of a giant billboard in Times Square to reveal who got the coveted spot on the front.

"Nobody knows until the last minute who the cover will be," a beaming Shayk, 25, told the AP following the announcement. "And then I saw it, and I couldn't believe it."

Also featured in this year's issue are last year's cover girl, Just Go With It star Brooklyn Decker, and Sean Penn's gorgeous ex, Jessica White.

On Thursday Casey Affleck fessed up to what many already believed: his brother-in-law Joaquin Phoenix's bizarre behavior on The Late Show with David Letterman last year was all an act.  But Affleck, who has directed a documentary about Joaquin, insisted that only he, the actor and the actor's agent really knew what was going on.

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Not so, RadarOnline.com has learned.

VIDEO: Joaquin Does Letterman

Late Show writer Bill Scheft told Nuvo magazine, “Dave knew about it, and Dave loved it because he could play along…it was great television.”

Scheft actually made the assertion to the small magazine late last year but his claim was largely ignored.

He said at the time, "I’ve told people that [everyone is 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 [River, who died of a drug overdose in 1993]. I said no. I saw the segment notes. It’s an act. I saw Ben Affleck’s brother taping the whole thing from offstage.”

In light of Affleck's admission that it was all an act, Scheft's claim about Dave being in on it has taken on new credibility.

"I'm Still Here: The Lost Year of Joaquin Phoenix," is the name of the Affleck docu.  The actor-turned-director is being sued for sexual harassment by two women on the film's staff.

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It should all make for more "great television" Wednesday night when Phoenix again appears on The Late Show.

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Star power was in full effect on The Late Show with David Letterman on Tuesday night, as the late night talk show host invited two sexy guests to share the spotlight. Katy Perry and Drew Barrymore were both dressed to impress, but only one of them shined the brightest!

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Katy Perry showed off her flawless bod in a bright coral bandage mini, which featured crafty straps. The sassy songbird paired the attention grabbing number with Christian Louboutin Jeannette spiked sandals and oodles of colorful, tribal-inspired jewels.

PHOTOS: Drew Barrymore Dazzles At The Going The Distance Premiere

Drew dazzled in a sequined copper top, which she paired with high-waisted, front pleated pants, the same Yves Saint Laurent Trib Two’s she wore to the Going the Distance premiere on Monday night and a Samantha Willis Bowery ring.