“My best friend forever,” she wrote alongside a photo of her as a baby, with a toddler Finneas looking at her from the right. “Will never love anyone as much as I love you @finneas happy birthday you are the best thing i have.”

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Fans in the comments were overwhelmed by the sweet sentiment and adorable photo. “Literally best friends forever. The duo that keeps on giving us magical and beautiful music. I cannot imagine the music world without ya’ll.”

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Someone else put, “You both are so unique. the best duo. Finneas deserves the world and so do you billie. happy birthday Finneas.🤍” and “Crying”, as well as “The best duo out there.”

Back in 2019, Billie thanked her brother in an acceptance speech for Variety, saying he was “probably the only reason I’m alive.” She said, “A big thank you to my big brother Finneas. Finneas is my best friend, my big brother, he’s four years older than me and we’ve been best friends forever.

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“We started making music together when I was 13 and he was 17; he produces everything. He’s the only reason I’m anywhere in the whole world and he’s probably the only reason I’m alive.”