Piven tweeted to his fans on Wednesday, letting them in on a special deal for those coming to watch the 11:40 p.m. showing of the new film.
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And Piven kept that promise. He bought the whole theater popcorn before the show.
He took time to pose for photos with fans - and even took part in a big selfie with the crowd.
Piven showed up with an "Entourage" of his own - the film's writer and director Doug Ellin.
Piven won a Golden Globe and three consecutive Emmys playing abrasive but loveable talent agent Ari Gold for eight seasons on the smash HBO series, which came to an end in 2011.