Birthday girl Kristen Stewart was on The Tonight Show with Conan O'Brien where she got a chance to throw some shade at Justin Bieber. The jokester threw some shade towards Justin Bieber with a surprising diss after mocking him in a new Jenny Lewis music video.

The 25-year-old Still Alice star on the April 8 episode of the late-night talk show where host Conan O'Brien showed a video of KStew mocking Justin's "swagger" and make fun of his mustache in the video.

In the Jenny Lewis‘s music video, "Just One Of The Guys," Kristen Stewart was dressed up like a boy in an Adidas track-suit, ballcap and she sported a mustache.

After showing the video, Conan said her look reminded him of a pop star who is none other than Bieber. "It very much felt like you were doing a Justin Bieber - there was some Justin Bieber in there," Conan said, adding "Minus the mustache."

"In his dreams," Kristen quickly shot back, before realizing that she just laid out a pretty sharp insult against the Biebs and his own "mustache." Kristen looked embarrassed after cracking the joke and covered up her face with her hands before saying she didn't really mean it.

"I don't know where that came from. That was such a cheap, stupid joke," she said.