(Photo credit: @selenagomez/Instagram)

Kate Middleton may have given birth to the royal heir yesterday, but it was a big day for Selena Gomez too! The "Come & Get It" singer celebrated her twenty-first birthday with friends at Bagatelle in West Hollywood.

"Thank you to bagatellela for an amazing bday!!!!" she wrote on Instagram. "It's a birthday WEEK!"

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For the big night, Gomez, who just released her new album, "Stars Dance," was joined by 20 friends and family members, including her mother, her "Spring Breakers" co-star Ashley Benson and actress Francia Raisa, for a private dinner at the French bistro. (No, Gomez's on-again, off-again beau Justin Bieber was not in attendance!)

According to a source, the group enjoyed the Caesar salad, tuna tartare, Parisian gnocchi with truffle sauce and the restaurant's signature dish, the whole truffle-roasted chicken. For dessert, they dug into a "Mega Sundae" and of course, birthday cake.

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Says the source: "Selena had a great time!"

As was the case throughout the day. Before her big dinner, Gomez enjoyed Jack n the Box tacos and tweeted, "Guess what … I'm 21. UM, #turnupNOW" along with a photo of herself laughing with a group of friends.

"Safe to say, I'm enjoying this very much ;)" she added. "THANK YOU for all the bday love! I love you guys so much x."