20 celebrities you didn't remember were on 'Gossip Girl'

The CW

"Gossip Girl" was full of fun cameos and guest stars. The CW teen drama ran for six seasons and featured a ton of celebrities.

Before he was in "The Social Network," Armie Hammer was a jerk who messed with Blake Lively's Serena van der Woodsen, and "Jessica Jones'" star Krsyten Ritter played Lilly's sister in flashbacks. Then, you've got some cameos from model Karlie Kloss and Lady Gaga playing themselves. 

In honor of the show's 10th anniversary September 19, here's a look back at some of the best celebrity surprises. 

Lady Gaga performed her song "Bad Romance" as part of a performance art piece on the show's third season.

The CW and Alberto E. Rodriguez/Getty Images

Watch the scene. 

Model Karlie Kloss plays herself attending a fashion party on the premiere of the fourth season.

The CW and Dia Dipasupil/Getty Images

Watch the scene.

Armie Hammer plays Gabriel, a jerk who pretends to date Serena van der Woodsen to get at her money.

The CW and Alberto E. Rodriguez/Getty Images for Entertainment Weekly

Watch a scene. 

See the rest of the story at Business Insider