Somerset, UK - Billie Eilish said it is a "really dark day for women in the US" during her history-making Glastonbury headline set, the same day the Supreme Court ended the country's constitutional right to abortion.

The 20-year-old singer's comments come after the US court decided to overturn the landmark 1973 Roe v Wade case that legalized abortion nationwide.

During her set on the Pyramid Stage on Friday night, she spoke out against the ruling as she introduced her song Your Power, which explores people abusing their power.

Seated alongside her brother and co-writer Finneas O'Connell, she said: "The song we're about to do is, I think, one of the favorites that we've written, and it's about the concept of power and how we need to always remember how not to abuse it.

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"And today is a really, really dark day for women in the US. I'm just going to say that as I cannot bear to think about it any longer in this moment."

This appearance was particularly poignant for the singer, as she became Glastonbury Festival's youngest ever solo headliner.

During Billie's electrifying set, she treated the audience of adoring fans to a selection of hit songs from her two number-one albums, including Bury A Friend, When The Party's Over, NDA, and My Strange Addiction.

She gave a typically energetic performance, running and dancing across the stage, wearing a black and white graphic tee-shirt outfit with black striped arm-warmers and her hair in space buns.

The singer delivered another political moment, as she has in the past, during the set as she spoke of how society needed to better protect the environment.

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Ahead of performing Everything I Wanted, she said: "So I think we all know that we really need to do a better job of protecting the planet that we all live on.

"We always can do a better job of protecting our people and our friends and family and strangers and standing up for each other and standing with each other.

"And I love you all and I stand with you and I support you and everything that makes you who you are."

The audience appeared to reciprocate back her affection as throughout the set they sang, danced, and chanted her name.

Near the end of her set she admitted she felt "so undeserving" of this opportunity as she thanked the festival and the fans for having her.

She added: "I am so honored to be here among all of you and all the incredible artists and the history of this festival."

Eilish closed her history-making show with an explosive rendition of her hit track Happier Than Ever.

The singer energized the crowd as she delivered the dramatic chorus line which had the crowd screaming the lyrics alongside her. She amplified the energy as fireworks exploded across Worthy Farm in the British county of Somerset to end the first day of performances at the festival.

Indie-rocker Phoebe Bridgers also called out the SCOTUS decision during her set at the festival.

"Are there any Americans here? Who wants to say 'F**k the Supreme Court' on three?" she said, as she led the crowd in a chant.

On Saturday, the music festival will also see a milestone on the opposite end of the age spectrum. Sir Paul McCartney will become the oldest solo headliner when he takes to the main Glastonbury stage to headline on Saturday, exactly a week after celebrating his 80th birthday.