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."
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.