Billie Eilish's Family, Boyfriend Jesse Rutherford Celebrate Star's 21st Birthday During L.A. Show

Matt Winkelmeyer/Getty Images Billie Eilish

Billie Eilish might sing about "when the party's over," but this weekend the party was just getting started!

The music superstar was joined by her family and boyfriend Jesse Rutherford on stage at Inglewood, California's Kia Forum Friday — when they surprised her with a cake at her final of three "Hometown Encore" shows ahead of her 21st birthday on Sunday.

With her family by her side, and fans singing along, Eilish blew out her candles to the applause of the crowd, before giving her folks a hug.

"Want to take shots? Give me two days," Eilish joked with concert attendees after her family, including brother Finneas, left the stage. "I am 21 in two days, it's f---ing unbelievable."

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The show later saw Eilish joined on stage by Donald Glover — a.k.a. Childish Gambino — and her longtime collaborator, Khalid. With Glover, 39, Eilish let the artist take center stage for a full performance of his 2016 hit "Redbone," before he asked the crowd to wish her a happy birthday.

During a 2019 interview, Eilish revealed that Gambino "created" her. "That's a God," she said at the time. "You can't even put him on a list with other people."

Eilish also shared a performance with Khalid, 24, of their collab "Lovely" during his stint on stage, before he ran through his solo smash "Location."

The star later got into the holiday spirit and performed a rendition of "Have Yourself A Merry Little Christmas" — which she did earlier in the week as well.

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During Thursday's show at the Forum just a day before, Eilish surprised her fans with guest appearances by Dave Grohl and Phoebe Bridgers. With Grohl, 53, she sang a cover of the Foo Fighters' 1998 hit "My Hero."

"You know, I have to say, earlier this year, all of Foo Fighters' families gathered together at my house to watch the Grammys, and when Billie came out for her performance in the Taylor Hawkins T-shirt, the room was filled with real tears of love and gratitude," Grohl said at the show.

He added: "So from our families, who are here tonight, the Hawkins family, and everyone, we'd like to thank you very much for that. So let's sing it for Taylor. This song's called 'My Hero.' "

With Bridgers, 28, Eilish duetted on her 2017 track "Motion Sickness," where Eilish handled harmonies along with the second verse.

RELATED: Finneas Reacts to Sister Billie Eilish's Relationship with Boyfriend Jesse Rutherford: 'I'm Happy'

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And while Eilish was joined on stage by her new boyfriend Rutherford, 31, it wasn't the first time the pair appeared with each other publicly.

The couple previously made their red carpet debut in a Gucci blanket back in November during the LACMA Art + Film Gala 2022.

As part of her latest Vanity Fair interview, titled "Same Interview, Sixth Year," the pop star opened up about dating The Neighbourhood vocalist. "It's really cool and I'm really excited and I'm really happy about it," Eilish said of her relationship.

"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---ing f---er alive, but pulled his ass! Are you kidding me? Can we just [get a] round of applause for me?" she added. "Thank you, Jesse Rutherford, everyone."