John Mayer gushes about Katy Perry: 'What a cool voice'

Seems like John Mayer and Katy Perry can't stop gushing about one another. But, that's not necessarily a bad thing.

He's the latest confessor, chatting with Billboardabout how the couple collaborated on his little love ditty Who You Love, which leaked online last week. Mayer called on Perry to lend her voice to the tune, which is all about being upfront and not running away from the person you love.

"I immediately thought about Katy and I was like, what a cool voice. What a cool artistic personality to have on," Mayer says. "It was a really fun opportunity for her to write like, her answer to that. So you get these two sides to this relationship that are brutally honest but no less universal."

Mayer also lent some insight into Perry's new single Roar, which also leaked and has hit the top spot on iTunes, leaving Lady Gaga's latest tune Applause in the No. 3 spot, behind Robin Thicke's Blurred Lines.

"I remember hearing (Roar), going like, 'Wow what an interesting experience' to hear something that you identify as massive before it's massive," he says. "I thought it was a really sweet, unforgettable sort of experience to hear someone's work while they still have a very nascent relationship with it."