Singers Katy Perry and Taylor Swift used to have mad love towards one another until everything went south and there's nothing more between them than bad blood.

But recently, Perry has opened the doors of a possible collaboration with Swift - on the condition that the 26-year-old hitmaker apologizes to her, according to Entertainment Weekly.

On Saturday, the 31-year-old songstress responded to one fan's query about whether or not she is willing to do a collaboration with Swift in the near future. ""If she says sorry, sure!" was Perry's response to the fan named Camille.

Back in 2014, the year when Swift's fifth studio album "1989" was released, the singer admitted that "Bad Blood" was about a feud with a fellow female singer, whose name she didn't disclose. "She did something so horrible," Swift said in an interview with Rolling Stone. "I was like, 'Oh, we're just straight-up enemies.'"

Swift explained that their feud was not about a guy, but rather about business. "She basically tried to sabotage an entire arena tour. She tried to hire a bunch of people out from under me," she revealed.

In response, Perry cryptically tweeted: "Watch out for the Regina George in sheep's clothing." She then hinted in a later interview with Billboard that she was referring to Swift with that tweet. "If somebody is trying to defame my character, you're going to hear about it," Perry said at the time.

Their feud was taken to a whole other level courtesy of Swift's ex-boyfriend, DJ Calvin Harris, after he name-dropped Perry during a lengthy Twitter rant slamming his former flame. "I know you're off tour and you need someone new to try and bury like Katy ETC but I'm not that guy, sorry. I won't allow it," the DJ said in the now-deleted post.

Swift has yet to comment about Perry's latest tweet.

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