The singer-songwriter, real name Charlotte Aitchison, coined the cultural moment following the release of her sixth studio album titled Brat, which references an effortless "it" girl state of mind, characterised by neon green on her album cover.
British stars including model Cara Delevingne and TV presenter Tan France were among those celebrating the new remix of the track Guess, featuring Grammy and Oscar-winning musician Eilish.
View this post on Instagram A post shared by Charli (@charli_xcx)
A music video for the track, directed by Aidan Zamiri, saw the pair climbing up a mountain of lingerie, with Eilish driving a bulldozer.
"Thank u for letting me be a part of dis," Eilish said, sharing the music video on Instagram.
Charli XCX teased the Guess remix earlier in the week, posting a photograph of her standing with a guest artist with their faces cropped out.
However, fans were quick to deduce it featured What Was I Made For? singer Eilish, as she wore the same rings during her Chicken Shop Date interview with Amelia Dimoldenberg.
It comes after Charli XCX was nominated for the Mercury Prize album of the year award following the release of Brat.
Charli XCX was nominated for the Mercury Prize album of the year award for Brat. (Bianca De Marchi/AAP PHOTOS)
After the announcement that Kamala Harris would replace Joe Biden as the Democratic nominee for US president, Charli XCX posted to X: "Kamala IS brat".
The Biden-Harris campaign account changed its banner to Kamala HQ, using the same font and neon green background as the Brat album cover.
Eilish's debut record When We All Fall Asleep, Where Do We Go? was released in 2019, while the follow-up titled Happier Than Ever was released in 2021.
She most recently released her third studio album titled Hit Me Hard And Soft, with a new tour featuring UK dates scheduled for 2025.
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