The star changed one of the lyrics to say "I`ve been Glastonbury dreaming", prompting a huge roar of appreciation.
"You look amazing!" she screamed as the song reached its coda, before inviting the audience to sing with her.
"Glastonbury means the world to me, I`m not even lying," she said later. "I`ve always wanted to do this my whole life but I`ve been too scared."
She then found a young girl in the crowd and told her she`d been coming to the festival "since I was your age" and invited her on stage for an impromptu selfie.
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