Ben Stiller’s impersonation of Joaquin Phoenix at the Oscars was a last minute addition to the show – because the Tropic Thunder star refused to stick to official script.

Stiller appeared alongside Natalie Portman to introduce the nominees for the Best Cinematography award at Sunday’s (22Feb09) Academy Awards ceremony in Los Angeles.

And Stiller shocked the star-studded crowd by wearing a scruffy fake beard and wandering aimlessly around the stage, mocking Phoenix’ recent string of bizarre public appearances since the Gladiator star ‘quit acting’ to focus on his rap career.

But the gag only made the cut because Stiller had “a meltdown” at rehearsals on Saturday, “because he was unhappy with the script and decided he could do better,” according to New York Post gossip column PageSix.

A source tells the publication, “Ben refused to tell them what he planned until he arrived at the Kodak Theatre, and then he did that Joaquin Phoenix bit.”

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