The 'Roar' singer posted a message on Monday night (19 August) urging her followers to listen out for John's latest album Paradise Valley, which features a special duet featuring herself.
Katy tweeted: "Something VERY special is happening @ midnight EST tonight on ITUNES! My incredible, inspiring boyfriend @JohnMayer will release a spectacular record called, PARADISE VALLEY."
And, giving a nod to her duet with John, she added: "My favourite track is number six!"
Katy and John co-wrote and sing together on a track called 'Who You Love'.
Speaking about the track, John told Billboard: "When you first read the reports about [the duet], you'll think that it's a gimmick ... I love a good challenge and that's certainly one. But the hope is you hear it once because of the curiosity and then you go, 'Wow, I really like that. I could find a place for hearing that a lot more."
Katy, meanwhile, is gearing up for the release of her own album, Prism, on 22 October.
The first track from the record, 'Roar', has already been released and shot to the top of charts around the world, becoming Katy's biggest ever debut on iTunes.
Watch Katy's fabulous lyric video for 'Roar' below: