In a tweet to fans on Monday afternoon, she wrote, "FYI ALL UK & IRELAND RELATED SHOWS @CalvinHarris will NOT be joining in on the fun and has CANCELLED last minute."
Calvin Harris then launched a scathing attack on Katy Perry, insisting he had good reason to axe his slot - explaining he didn't want to perform with no production on stage.
In a series of messages he writes, "Sorry to all who wanted to see me with Katy - her team suddenly moved the goalposts, and i was to appear on stage with "no production".
"It would have looked s**t, sounded s**t - trust me you would have been more disappointed SEEING the show than u are with me cancelling. That's the honest truth. Her show is AWESOME, you'll all have an amazing time without me. (especially w/o (without) me DJing on a cardboard box in front of a pink curtain)."
But Katy Perry was left unimpressed with his explanation, insisting Calvin Harris has become synonymous with being unreliable, responding, "Funny the goal post seems to be perfectly fine for New Young Pony Club, Yelle, Robyn, Marina & The Diamonds to name a few... Or how bout Janell Monae (sic) and her 16 piece band... Etc... it's fine, I'm used to you cancelling on me, it's become ur staple!"