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PA
Hours before she was due to take to the stage, Demi Lovato has cancelled her Sunday night show in London due to swollen vocal chords.
The US singer had been due to perform at the O2 arena but has now been rescheduled to Monday 25 June.
Posting on Twitter at 17:17 BST on Sunday, the star said: "It breaks my heart to let you down."
She explained that she was "very, very sick" and had been examined by an ear, nose and throat doctor.
Lovato said she feared performing on Sunday could injure her vocal chords and lead to the rest of her tour being cancelled.
On Twitter she said: "I'm so so so sorry to disappoint any of my fans in London that have travelled hours to be here by plane or car, and to all of the fans that got these tickets for their birthday, holiday or any other special occasion.
"It breaks my heart to let you down. Just know I feel your frustration and I wouldn't do his unless I absolutely had to.
A statement from concert producer Live Nation confirmed the postponement.
"The show will now take place on Monday June 25th," the company said.
"All tickets will remain valid for the new date. Please contact your point of purchase for all ticket inquiries."
Fans of the singer responded with messages of support.
Lovato is due to perform four other UK shows - in Birmingham, Glasgow, Newcastle Upon Tyne and Manchester.