You might be more familiar with the Twitter spats Katy Perry and Calvin Harris shared with Taylor Swift, but way back in 2011, the pair got into a heated argument with each other over the DJ supporting her on tour.
It all kicked off in March 2011 when Katy tweeted, 'Calvin Harris will NOT be joining in on the fun and has CANCELLED last minute,' following plans for him to join her California Dreams Tour.
Calvin replied, "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", to which Katy hit back, "The goalpost seems to be perfectly fine for New Young Pony Club, Yelle, Robyn, Marina & The Diamonds, to name a few.
"It's fine, I'm used to you cancelling on me, it's become ur staple! [sic]"
Seeing as Katy featured on Calvin's track 'Feels' alongside Pharrell Williams and Big Sean earlier this year, it was assumed the pair had managed to put their differences aside and the feud behind them.
But what did they kiss and make up over? Not Taylor Swift, actually, but rather their desire to collaborate with each other.
During an interview with On Air With Ryan Seacrest, Katy explained, "We just bumped into each other and he said, 'I think I have a song that you should come check out'.
"I was like 'cool' because we had always meant to work together for years and years and years. I came to the studio and he played me a bunch of unfinished but really solid moments for his new record.
"Then he played me this one part for this new song called 'Feels' and I was like, 'Oh yeah'. This is like my favourite song off the record. I was just down to do it. I've always wanted to collaborate with him for years and years and years.'
Wonder if it was TayTay's favourite song on the record, too.
