Uinterview - u ask. they tell.

Nothing drives teenage girls crazier than Justin Bieber, unless, of course, it’s Justin Bieber and Miley Cyrus...together.

Bieber performed for a sold-out crowd at Madison Square Garden Tuesday night, tweeting beforehand “Its all really coming 2gether. Tonight I perform with my heroes! MSG its almost time!”

The screaming crowds had no idea what was in store for them. The first of the parade of famous guest stars was R&B favorite Boyz II Men, on an a capella rendition of their hit “On Bended Knee.” Then Bieber’s mentor Usher appeared for their collaboration “Somebody to Love” off Bieber’s album My World 2.0. Cyrus sang with Bieber on his song “Overboard,” prompting general hysteria in the arena. Will Smith’s karate kid Jaden made an appearance, as did as rapper Ludacris.

The entire concert was filmed for Bieber’s upcoming 3D biopic, which will be directed by Step Up 3D’s Jon Chu. —AMY LEE