Katy Perry would be willing to collaborate with Taylor Swift one day on one condition: if the 1989 singer apologizes.

This is what Perry revealed Saturday night when one fan tweeted, “Will you collab with Taylor Swift.” “If she says sorry, sure!” Perry responded.

In 2014, Swift told Rolling Stone her 1989 track “Bad Blood” was about an unnamed fellow singer. “She did something so horrible,” Swift said at the time. “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.”

Soon after the story went live, Perry tweeted, “Watch out for the Regina George in sheep’s clothing,” and later hinted to Billboard that she was indeed referring to Swift. “If somebody is trying to defame my character, you’re going to hear about it,” she said in a 2015 interview.

Then in July, Swift confirmed that she co-wrote Calvin Harris and Rihanna’s “This Is What You Came For” under a pseudonym, which Harris responded to on Twitter with a reference to Perry. “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,” Harris, who dated Swift up until this past June, wrote in the since-deleted post. “I won’t allow it.” 

Not long after, Perry tweeted a gif of Hillary Clinton giving a knowing look and then retweeted a post of her own that said, “Time, the ultimate truth teller.”