But the British singer didn't announce it via an official press release. Instead, she just told her fans during a concert at London's O2 Arena on Friday night. The news then went viral on social media.
"Who's going to Glastonbury this year?" she reportedly asked the crowd. "See you there. I'll be there. I'll be headlining on the Saturday night this year."
Glastonbury Festival, which this year runs from Jun. 22 to 26, confirmed the news on Twitter soon after:
According to the NME, Adele said she'd wanted to headline in 2015 but decided not to because her new album -- "25", released in November -- wasn't quite ready.
She also had a message for people who think her ballad-heavy music isn't suited to the more hippy and rock ethos of the five-day event at Worthy Farm in Somerset. "And to the people who say I am too boring to headline, you're more fucking boring for moaning about me headlining."
The "Hello" singer will headline the festival's iconic Pyramid Stage on the Saturday night, following on from Muse on the Friday and before Coldplay -- which closes the festival on the Sunday. Kanye West was the main attraction in 2015.