Inside Harry Styles' 21st Birthday Party: Jennifer Lawrence, Kendall Jenner, Cara Delevingne and More Attend Star-Studded Bash

This may just top Taylor Swift's 25th birthday bash (and that's saying a lot, considering Beyoncé was present). 

Harry Styles celebrated the big 2-1 on Saturday evening at new Hollywood hotspot Isabel's, which opens this week. 

In true pop star fashion, a number of A-lister joined the One Direction boybander, including on-again couple Chris Martin and Jennifer Lawrence, Adele, Adam Levine, Kelly Osbourne, Cara Delevingne and Kendall Jenner. 

The super-private soiree was kept top secret, and no paps were allowed at the star-studded bash, where guests goofed around in a fun photo booth and gave us a sneak peek of the party by posting pics on Instagram. 

The handsome 1-D star enjoyed not just one, but four birthday cakes from bakery Sweet Lady Jane, which were adorned with photos of the birthday boy. 

Additional celebs at the party included Alexa Chung, Zach Braff, Samantha Ronson, Rashida Jones, Cacee Cobb and Donald Faison, Rita Ora, Ricky Hilfiger, Kimberley Stewart, Tom Morello, Cindy Crawford and Rande Gerber (remember, Styles has previously made pizza with their children, Kaia and Presley). 

Oddly enough, Styles has been romantically linked in the past to both Delevingne and Jenner (and heck, even Kimberly Stewart) although the BFFs clearly didn't have any qualms over joining forces to celebrate their pal. 

The 22-year-old British supermodel even posted a pic with Jenner, Osbourne, Ronson and Rashida all lined up in order of their height. 

And Kelly also shared a few shots--in which Styles even makes a cameo!--while messing around in the photo booth with Rashida and Cara. 

Looks like a blast! Happy Birthday, Harry (stay hot!).