[Source: BBC Entertainment]

Ten thousand pairs of underwear which were used in Charli XCX and Billie Eilish’s latest music video have been donated to charity.

Guess, a remix of the Brat original, dropped on Thursday night and showed Billie smashing into a party on a bulldozer surrounded by thousands of bras and knickers.

During the video’s credits, a message appears saying all the unworn garments would be donated to I Support The Girls.

The US-based charity works internationally to distribute underwear and period products to women experiencing domestic violence, homelessness and hardship.

As the pair sing: you wanna guess the colour of my underwear/ you wanna know what I’ve got going on down there – more and more pairs surround them, strewn across the street and falling from the sky.

The charity says it has received 10,000 pairs which have “overtaken” its warehouse.

“We’re so lucky to be getting the formidable panty mountain,” the charity posted on X, referencing the huge pile of underwear Charli and Billie climb towards the end of the music video.

Its founder, Dana Marlowe, tells BBC Newsbeat the donations “feel very in line with Brat summer”.

“Charli XCX and Billie are both top of their game and they’re showing women empowering women,” she says.

“They’re on top of bra mountain and they’re on top of their industry and they’re not forgetting that there are charities that can do something with the excess props in a music video.

“It really becomes an incredible cyclical effect of women supporting women supporting women which is absolutely part of Brat summer.”

Importantly, she says, a lot of the underwear in the video that’s been donated is “sexy” too.

“At first glance, you might think, why would a nonprofit organisation want to receive that?,” Dana says.

But for I Support The Girls, an important part of their ethos is finding dignity and power in choice, she says.

“There’s people for every style. Just because somebody is experiencing homelessness doesn’t mean that they don’t prefer to wear a thong.”

Guess is Charli’s second collab remix on her critically acclaimed album Brat after releasing a version of Girl, So Confusing with Lorde last month.

But it’s a rare collaboration for Billie, who told Zane Lowe earlier this year that it was her first time working with another artist in about six years.

On Instagram, the Bad Guy artist thanked Charli for letting her work it out on the remix to which Charli responded: “tysm for being on this track I’m beyond honoured.”

“Love and respect forever.”

Charli teased new music last week but speculation surrounded a potential collaboration with Chappell Roan after she posted a selfie on Instagram holding a Brat CD.

Brat has been nominated for this year’s Mercury Prize and Brat summer has taken off online, with even US presidential nominee Kamala Harris getting in on the trend.

It’s Charli’s sixth studio album and debuted in the top 10 on both the UK and US.

Billie’s also released new music this year with Hit Me Hard And Soft, which came out in May.

BBC Newsbeat has contacted representatives for Charli XCX and Billie Eilish for comment.