katy perry taylor swift
Katy Perry and Taylor Swift have been feuding for some years now Getty

Katy Perry is ready to collaborate with Taylor Swift, but has a condition. The Roar hit-maker wants an apology from the 26-year-old.

Twitter was abuzz after a fan asked Perry whether she would collaborate with her longtime nemesis Swift. She replied: "If she says sorry, sure!" The 31-year-old singer took to Twitter on 10 September to let her fans know that she would make music with the Blank Space hit-maker if the latter apologised.

"WOAAAHHH," one fan wrote, while another added, "@katyperry's responses to tweets are perfect!"

The two singers have been feuding for some years now. Swift's hit single Bad Blood is believed to be about Perry. When Swift's close friend Selena Gomez was asked if the song was about Perry on Watch What Happens Live, she declined to comment.

"Time, the ultimate truth teller," Perry wrote on Twitter in May 2015, when Swift first revealed she had been betrayed by a fellow female artist. "For years, I was never sure if we were friends or not. She would come up to me at awards shows and say something and walk away, and I would think, 'Are we friends, or did she just give me the harshest insult of my life'?" Swift told Rolling Stone in September 2014 referring to Perry.

"She did something so horrible," Swift said, speaking about an incident involving Perry that happened in 2013. "I was like, 'Oh, we're just straight-up enemies.' And it wasn't even about a guy! It had to do with business. She basically tried to sabotage an entire arena tour. She tried to hire a bunch of people out from under me. And I'm surprisingly non-confrontational – you would not believe how much I hate conflict. So now I have to avoid her. It's awkward, and I don't like it."