The show will now take place on June 25 instead.
The 25-year-old sent her fans a heartfelt message and told them she was "very sick".
'If I go on tonight and injure my vocal chords any more I could potentially have to cancel the rest of my tour'. "I'm so so sorry to disappoint any of my fans in London that have traveled hours to be here by plane or auto, and to all of that fans that got these tickets for their birthday, holiday or any special occasion", she added.
In an emotional text post and video posted to her social media, Demi - who had performed the day before at Capital FM's Summertime ball - detailed how if she tried to carry on, there was a good chance she would have to cancel the rest of her world tour.
'It just breaks my heart to let you down.
While a third added: 'Take good care of yourself, I'm sure everyone will understand and we know how much you love us, and how much it tears you apart when these things sadly happens.
Her biggest songs to date include "Confident" and "Let It Go", plus her recent hit "Sorry Not Sorry". Just know I feel your frustration and I wouldn't do his unless I absolutely had to. The pop star ended her note by telling her followers that the concert has been rescheduled for June 25, writing: "Thank you for understanding".
"So refunding those train/plane/bus tickets people have forked out so they can come see you on a WEEKDAY yeah?", one fan wrote. "Probably can't even come to the next date FUMING - understand you're not well but not a few hours before the event".
Lovato appears to have some bad luck surrounding this tour.
Here's hoping for a speedy recovery for Lovato - particularly since she's set to play a show in Birmingham, England, in just two days.
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