Selena Gomez is finally legal, for the starlet turned 21 today, Monday, July 22. 

The "Stars Dance" singer decided to celebrate her milestone birthday with a party in Los Angeles on Saturday, according to Hollywood Life. 

Gomez had on a sexy, short black dress, complete with red lipstick and devil horns as her "birthday suit." But the best part was that her friends including Lily Collins and Julianne Hough presented a cake wtih leopard-print frosting, images of Gomez and Justin Bieber's photo on it, "she loves Justin," a source told HL.

"So he went on the cake," the source continued.

Bieber missed his reported on and off-again girlfriend's party. But he was there in spirt given the picture reminder.

HL reported that the Biebs missed being there for some shirtless fun at a Toronto pool party. He danced, drunk and posed with "hot girls in bikinis" on the same day that Gomez told Ryan Seacrest that she was single in an E! special that aired on Sunday.

Regardless of her relationship status, Gomez was happy about being legal. On May 30, the Adidas NEO designer had revealed that the big 2-1 was huge for her, "Obviously in America 21 is the age," she said to Canada's MuchMusic, reported HL.

"So actually gonna have a huge party," she continued. "I wanna have a great party - I'm going to invite my friends and my family, and I'm definitely going to celebrate."

She also celebrated with her fans by releasing a new music video for the song, "Birthday."

Check out the video and tell us what you think in the comments section below!