Billie Eilish Gets Sweet 20th Birthday Tribute from Brother Finneas: 'The Joy of My Life'

Finneas/Instagram; Inset: Rodin Eckenroth/FilmMagic

Happy Birthday, Billie Eilish!

On Saturday, the singer celebrated her 20th birthday and received a special Instagram tribute from her older brother, producer, and best friend Finneas O'Connell.

"20!!!!!!!!! Watching you grow and become the thoughtful, incredibly kind, talented, hilarious and hardworking person that you are today has been the joy of my life!" Finneas, 24, wrote alongside two photos of his sister.

"I'll be your #1 fan till the day that I die," he continued. "There is truly nothing I love more than being your big brother. Happy birthday!!!"

RELATED: Billie Eilish Shares the Stage with Her Parents and Brother Finneas for Her SNL Musical Performances

Finneas' post also included a silly throwback clip of his sister jokingly "eating" their mother's hair as she laughed. The sibling duo's mom, Maggie Baird, later shared her own birthday tribute to Billie.

"Happy Birthday Billie Eilish Pirate Baird O'Connell! You are funny, and complicated, and goofy, and tough, and strong, and brilliant! Your joy for the holidays and all things birthday and Christmas, gifts so much joy to our family," she wrote. "How can someone be so powerful and so goofy and childlike at the same time? I don't know, but you make life more exciting and tender. I love you with ALL my heart and soul."

Billie and Finneas have been open in the past about their strong relationship.

They recently hit the stage together on last week's episode of Saturday Night Live for a haunting performance of "Male Fantasy" from her second studio album Happier Than Ever.

Will Heath/NBC/NBCU Photo Bank via Getty

When the Grammy-winning brother-sister duo made their first appearance on the comedy sketch show in 2019, Billie wrote a sweet message to her brother on Instagram, saying, "MY BROTHER IS MY BESTFRIEND AND WE DID SNL LAST NIGHT AND IT WAS A PEAK LIFE EXPERIENCE. WOW. THANK YOU LIFE FOR GIVING ME WHAT I HAVE."

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The musical siblings have worked together on many of her chart-topping hits and Finneas raved about Billie being a "true artist" to PeopleTV at the 2020 Grammys.

Samir Hussein/WireImage FINNEAS and Billie Eilish

"It's like, she knows exactly what she wants. She knows how to get what she wants. She knows what it'll take. She knows even clearer when something isn't quite right how to get it to where it needs to be. That to me is what a true artist is," Finneas said.

RELATED: The Sweetest Things Billie Eilish & Finneas Have Said About Each Other

"Even though we're all together making songs and I produce them, it's so her vision," he explained. "Especially when we walk out on stage every night. It's so meticulously thought through by Billie and I admire that endlessly in her."

Last month, it was announced that Billie and Finneas had written and produced three songs for the upcoming Pixar movie Turning Red to be performed by the film's fictional boy band 4*Town.