Drink alcohol and go clubbing. These are two of the many luxuries afforded to those who turn 21-years-old in the US, and they're two things Billie Eilish did plenty of to celebrate her milestone birthday this weekend.

The singer turned 21 on Sunday and decided to throw a huge birthday party to celebrate 'becoming an adult'. It was a star-studded guest list with A-listers such as Avril Lavigne, Doja Cat, Hailey Bieber, Justin Bieber, Kendall Jenner, Khalid and Childish Gambino all present.

Billy certainly celebrated in style and made the most of the new drinking luxuries afforded to her on this special birthday. "Want to take shots? I am 21 in two days, it's f**king unbelievable", said Eilish, to the delight of all those inside.

Completely loved up

The 'Ocean Eyes' singer was joined by her new boyfriend Jesse Rutherford at the party, and the pair looked totally loved up.

Rutherford, who is the lead singer of alternate rock band The Neighborhood, couldn't stop kissing his girlfriend all night. The pair constantly looked at each lovingly.

Santa Baby

There were plenty of impressive outfits on display on the night. The birthday girl was dressed in a sexy Santa outfit and wowed with her festive look.

Kendall Jenner and Hailey Bieber looked equally stunning. Jenner posted several photos of the night on her Instagram story with both Bieber and Eilish. They were taken in a photobooth that Billy had installed for guests to take pictures together. Fun times!