The producer-musician opened up to ET at the 2019 American Music Awards.
Billie Eilish has been revolutionizing pop music and changing the face of the genre with her massive hit debut album, When We All Fall Asleep, Where Do We Go?, and along the way she's been joined by her supportive older brother -- and producer -- Finneas O'Connell.
The siblings both turned out for this year's American Music Awards on Sunday, and O'Connell, 22, stopped to talk with ET's Keltie Knight about his relationship with his 17-year-old sister, and the massive public obsession with both her music and her unique style.
"I think it's awesome!" O'Connell said of seeing fans rocking clothing and hair choices influenced by Eilish. "I idolize my kid sister, so I get it. I understand why other people do too."
The pair have been by each other's side during Eilish's meteoric rise to superstardom, but that doesn't mean they don't have their occasional disagreements. However, because of their familial bond, they know how to move past them.
"You fight about everything, that's the deal," O'Connell said of siblings in general. "But that's the fun part!"
"Also, because there's so much love there, that doesn't matter at all, and nobody gets awkward or weird," he added.
As it turns out, most of their fights are just impassioned debates, and their clever way of moving past a fight is through humor.
"We're both trying to get a point across, and then one of us makes a joke and the other one laughs, and then that's it," he shared with a smile. "It's over."
Recently, the GRAMMYs revealed their full nominations list for the upcoming 2020 awards show, and Eilish broke a record for being the youngest artist to get nominated in the four major categories -- Album of the Year, Record of the Year, Song of the Year and Best New Artist, as well as two other nominations for Best Pop Solo Performance and Best Pop Vocal Album.
O'Connell, as her producer, shares a few of those nominations -- as well as Best Engineered Album - Non-Classical, and Producer of the Year - Non-Classic -- and apparently the siblings celebrated with some pyrotechnics.
"I think we lit off some fireworks we had left over from the Fourth of July that night," he said recalling how he and Eilish commemorated the exciting nominations. "Alone in the backyard."
"My dreams as a kid were so far below the GRAMMYs, like, maybe selling out a show, or, like, seeing your album on a shelf in an Urban Outfitters… and the GRAMMYs are so far above that," O'Connell shared. "It's very ridiculous."
During the show, the first category of the night, Favorite Alternative Rock Artist, Eilish beat out Imagine Dragons and Panic! At the Disco, and made sure to thank her brother at the end of her acceptance speech, telling O'Connell "I love you," after thanking her fans.