See how Britney Spears marked her 35th birthday

Friday's KIIS-FM Jingle Ball didn't just provide fans with an update on Kanye.

It also let them participate in Britney Spears' 35th birthday bash.

A giant bday cake was wheeled out following her set at Los Angeles' Stapes Center, which included Toxic, Slumber Party, Womanizer and I'm a Slave 4 U.

Watch as Ryan Seacrest leads the arena in a tone-deaf chorus of Happy Birthday.

And check out photos from her show and birthday bash below.