Katy Perry has been hinting that the sound of her new album is much more mature than her previous material.

She is working on the new record with songwriter pal Bonnie McKee who also worked with Perry on the hugely successful California Gurls.

McKee told MTV News: "I think it's a little bit more grown up and it's really interesting.

"I'm really excited for the world to hear it because she's just... she's taking a new approach. And I don't want to say too much about it, but it's definitely different. It's definitely a little more mature than the California Gurls of yesterday."

McKee has also worked with Perry on a number of her other hit songs including Last Friday Night (T.G.I.F), Part of Me and Wide Awake.

The pair have been friends for some time after meeting in a thrift store in Los Angles.

"Katy and I are really similar. That's kind of how we became friends. We met at Wasteland on Melrose [Avenue], a thrift store. We just are totally on the same level... We're just soulmates in that way, I guess," McKee recalls.

No other details are known about the album as yet.