Katy Perry found a kindred musical spirit in pop singer/songwriter Bonnie McKee. So when the "Fireworks" singer started working on her follow-up to 2010's Teenage Dream, she enlisted the help of her "California Gurls" co-writer to cook up some of that old magic.

"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," McKee told MTV News.

Perry seemed to be returning the favor when she appeared in McKee's first-ever music video, for [article id="1709797"]"American Girl," [/article] off her upcoming debut album. The twosome had already penned four #1 singles together: "California Gurls," "Teenage Dream," "Last Friday Night (T.G.I.F.)" and "Part of Me." And McKee says their long list of hits comes from their deep personal connection. In fact, at one point they both wrote songs called "The One That Got Away," both meant for Perry, without even realizing it. (Perry's own version made the cut for TD, meanwhile of a version of McKee's went to Miranda Cosgrove.)

She recalled, "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."

The two also teamed up for the more reflective "Wide Awake."And it seems that Perry is continuing to dig deeper on her upcoming album. Since Teenage Dream, Perry [article id="1689730"]married and divorced Russell Brand[/article] and made headlines with her [article id="1709220"]on-again, off-again relationship with John Mayer[/article], so it looks like she has plenty of material.

"I think it's a little bit more grown up and it's really interesting," McKee said. "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."