Bill Murray celebrated his movie “Rock the Kasbah” like a rock star by partying till after midnight Tuesday and jumping onstage with a band at the subterranean Hudson New York City club Good Units.

Meanwhile, we hear one guest who showed up at the bitter end of the night is Murray’s rumored younger love interest, indie rocker Jenny Lewis.

Murray booked the same band that played his son Luke’s September wedding, Chevy Chevis Entertainment, and he joined the group to sing the Rascals’ “Good Lovin’ ” for a crowd including Lady Gaga and Taylor KinneyKate HudsonNaomi Campbell, and Zooey Deschanel.

“Bill was basically the best party host ever,” said a spy. “He circled the room meeting everyone, pushing people onto the dance floor, and picking ladies out of the crowd and dancing with them. He spent most of the night getting his groove on.”

At an earlier AMC Loews Lincoln Square screening, where Jennifer Lopez also saw the film, Murray cracked to the crowd as Hudson walked down an aisle: “My God! She’s lost an enormous amount of weight.” He also interrupted the movie’s director, quipping, “Barry Levinson — You thought the guy was dead.”

At the later dance party, normally reserved Bruce Willis sang and danced his way though “Proud Mary.” Murray closed the bash dancing onstage to the Clash’s “Rock the Casbah” with screenwriter Mitch Glazer, and gave a speech thanking producer Steve Bing, quipping, “All you guys go shake his hand — all you girls go do whatever you think is right.” Also celebrating was distributor Tom Ortenberg of Open Road Films.

Spotted arriving to meet Murray and jumping onstage, too, was former child actress Jenny Lewis, 39. “Jenny is Bill’s special friend,” a source told Page Six. Flame-haired Lewis, who’s been linked to singer Johnathan Rice, was also at a Hamptons screening of the film, and the pair was seen together after at the Huntting Inn. She’ll appear in Murray’s upcoming holiday special and popped up in a faux rock doc to promote “Rock the Kasbah.” Her rep said, “No comment.”

A photo posted by jenny lewis (@jennydianelewis) on

This article originally appeared in the New York Post's Page Six.

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