Katy Perry creating new sound

Katy Perry's new album is more "mature".

The singer is currently working on her fourth record, the first since 2010's Teenage Dream.

Songwriter Bonnie McKee, who is one of Katy's closest pals and also worked with the star on smash hit California Gurls, promises big things.

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

"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."

Bonnie also worked with the Firework singer on tracks Last Friday Night (T.G.I.F.), Part of Me and Wide Awake.

The musician recalled how the two met and why their bond is so strong.

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

"We were just in [Katy's hometown of] Santa Barbara and we wrote three or four songs, I guess. So I have four songs with her coming out."

No details about the name of Katy's album or a release date are known yet.

Bonnie's other song-writing credits include Britney Spears' Hold It Against Me and Rita Ora's How We Do (Party).