Katy Perry could be running back to an ex-boyfriend - and no, it's not John Mayer.

The Sun reported that Perry and Rob Ackroyd, a guitarist for Florence + the Machine, have been spending quality time together in London. The "Dark Horse" singer and Ackroyd were spotted together at an after party celebrating the end of Perry's European "Prismatic" tour.

"Katy and Rob seemed to be very much back together at her party on Saturday night," a source told The Sun. "They were inseparable, kissing, flirting and cuddling away in front of the roadies, celebs and friends at the bash. There were a fair few famous faces in the room, but Katy and Rob only had eyes for each other."

However, an insider for Gossip Cop said that Perry and Ackroyd have nothing between them and are just friends. The pair briefly dated in 2012 after meeting at the Coachella festival, and remained close friends post-split, even during Perry's relationship with Mayer.

In May 2012, a source told E! News that the relationship was not serious and added that Perry liked "him a lot, but it was just a distraction. It was very short-lived, she's still dealing with getting over her marriage [to Russell Brand] and it's going to take her a while to truly be able to trust anyone again."

Ackroyd has reportedly been seen at several of Perry's events. He recently shared a picture on Twitter of Katy on stage with the caption, "Killed it."

"Katy and Rob are very close and have remained close since they broke up a while ago," a source told E! News. ''Rob has been in London for a while now.''