Stephanie Pratt Arrested On Suspicion Of DUI

'The Hills' star Stephanie Pratt (and sister of the infamous Spencer Pratt) was arrested on suspicion of DUI in Los Angeles at 3:45 am this morning after leaving Heidi Montag's birthday party.

Here's what Stephanie tweeted from Heidi's birthday party:

its my sissy @hollymontags bday party! just finished dinner and going to Empire but im pretty tired aka yes i am the party pooper :(

Sources reportedly told TMZ that Stephanie had just left the club when she was pulled over.

Our source says cops watched Stephanie get in her car and were waiting to bust her.

Sounds like they prevented a possible accident there! The police confirmed the arrest.

"It was your basic DUI. Our traffic officers driving down the street spotted her and pulled her over," Sgt. Sal Ogaz tells PEOPLE. "She was cooperative and there were no issues with her arrest."

Yet it sounds like the arrest caused some commotion outside the club.

So how's this for crazy. We're told some spectators who had just gotten out of a club saw Pratt get busted. Some started taking pictures, which ticked off some of the others and a big fight broke out on the street while Stephanie was being cuffed. But Steph was the only one taken into custody.

Stephanie reportedly is still in Van Nuys jail at this time; her bail was set at $5000. Surely brother Spencer can afford to help her out with that?

Photos by INF