Katy Perry is reportedly dating Florence and the Machine guitarist Rob Ackroyd.

The 'Roar' singer - who dated Rob back in 2012 after the pair met at the Coachella music festival - is said to have reunited with her former flame after spending time with him during the UK leg of her Prismatic World Tour.

Katy, 29, was spotted kissing and cuddling Rob at an afterparty in the exclusive backstage area of London's O2 Arena to celebrate the end of the European leg of her tour where the pair were surrounded by a host of celebrity guests including Cara Delevingne, Selena Gomez and Suki Waterhouse.

A source said: ''Katy and Rob seemed to be very much back together at her party on Saturday night.

''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.''

The 30-year-old musician also shared a picture of one of Katy's gigs on twitter praising the singer with the caption, ''Killed It.''