EXCLUSIVE: Ansel Elgort Celebrates 22nd Birthday With Wild 'Allegiant' Afterparty

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Ansel Egort cut loose for the big 2-2!

It seems the Allegiant star had a pretty raucous night (and cake!) at the afterparty for the film's premiere on Monday, which happened to land on the same day as the actor's birthday. A source tells ET, "The party was nuts."

"Shailene [Woodley] was 'dirty dancing,'" the source adds, referring to Ansel's co-star in the movie. "She changed into a tank top and jeans, and they were grinding in the middle of the VIP."

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Shailene apparently debated over whether to wear a dress for the big night, but ultimately opted for an Elie Saab jumpsuit, telling ET, "Dude, I am so all about pants life."

"Theo [James] was rowdy and doing these weird chants, Ansel dancing up on the tables," the source continues. "All sharing clove cigarettes."

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Ansel posted about the fun evening on Instagram on Tuesday, writing, "Last night at the Allegiant premier after party, surrounded by friends and family as they brought out a cake and sang. What a moment ."

The actor kept it very fashion-forward at the premiere, rocking a thick white collar that many mistook for a towel. Ansel showed off the style accoutrement in an Instagram video with the "Damn, Daniel" kids.

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Happy birthday, Ansel!

Allegiant hits theaters this Friday.

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