After struggling the past Wednesday and Thursday nights on stage, a doctor advised her to not perform in London.
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The cancellation comes after hinting to fans that her current tour could be her last.
Adele wrote an emotional open letter, saying "I'm so desperate to do them that I've even considered miming just to be in front of you and be with you. But, I've never done it, and I cannot in a million years do that to you."
She says refunds will be offered if the shows can't be rescheduled.