Billie Eilish dressed up as Santa to celebrate her 21st birthday at a lavish party with her celebrity friends.

The pop star marked the milestone on December 18 and she chose a Christmas theme for her bash at a swanky hotel in Los Angeles on Saturday night (17.12.22) with the singer posing at The West Hollywood EDITION venue in a bright red sleigh and wearing a Mrs Claus costume.

Billie was seen kissing her boyfriend Jesse Rutherford - who also wore a Santa suit - at the bash as the couple partied with guests including fellow pop starJustin Bieber and his model wife Hailey and musician Doja Cat.

Video posted online shows the couple on the dancefloor as Billie's friends gathered around her to sing 'Happy Birthday' as she's presented with a cake topped with candles and candy canes.

The DJ is also heard telling the group: "[Put your] mother f****** hands in the sky for Billie".

Other guests at the bash included reality star/model Kendall Jenner, pop star Avril Lavigne, singers

Olivia Rodrigo and Dove Cameron and actress Eiza Gonzalez.

The party came a day after she performed at Kia Forum in Ingelwood, California on Friday night (16.12.22) and was presented with a cake onstage by her family.

She blew out the candles and gave her parents a hug before they left the stage. The singer then told the crowd: "Want to take shots?. Give me two days. I am 21 in two days, it’s f****** unbelievable."

Billie recently opened up about her romance with The Neighbourhood frontman Jesse, telling Vanity Fair magazine: "It's really cool and I'm really excited and I'm really happy about it. I managed to get … to a point in my life … where I not only was known by a person that I thought was the hottest f****** f***** alive, but pulled his ass! Are you kidding me? Can we just [get a] round of applause for me? Thank you, Jesse Rutherford, everyone."