Billie Eilish brought out special guest Charli XCX to perform their 'Guess' remix in Los Angeles on Tuesday night (17.12.24).

The 22-year-old pop megastar surprised fans at the latest stop of her 'Hit Me Hard And Soft Tour' at the Kia Forum in Inglewood, California, with a performance of their hit collaboration from the album of the year, Charli's 'Brat'.

As 'Brat' green-coloured lasers lit up the room, Charli was seen twerking as Billie hyped up the crowd and fans went wild.

Wishing Billie a happy birthday on Wednesday (18.12.24), Charli captioned footage from their performance on X/Twitter: "love u billieeeeee and hbd!!! 3 (sic)"

The 'Guess' remix is nominated for Best Pop Duo/Group Performance at next year's Grammys.

Billie cheekily confesses she would have sex with Charli on their raunchy tune.

The 'Lunch' hitmaker - who identifies as queer - sings: "Charli likes boys, but she knows I'd hit it. Charli, call me if you're with it."

In the music promo - helmed by Aidan Zamiri - the pair are seen mounting a pile of lingerie with Charli singing: "You wanna guess the colour of my underwear."

At the end of the song, Charli, 32, sings "You wanna guess what me and Billie have been texting about... You wanna guess if I'm serious about this song."

As well as having fun on the playful song, the pair raised awareness for those from poor backgrounds and homeless girls who cannot afford essential items by donating the bras and knickers from the video to the I Support The Girls non-profit.

A press release read: "All bras and underwear used in the music video have been donated to I Support The Girls. ISTG collects and distributes essential items, including bras, underwear and menstrual hygiene products, allowing people experiencing homelessness, impoverishment or distress to stand tall with dignity."