John Mayer opened up about his collaboration with on-again girlfriend Katy Perry when he stopped by Jimmy Kimmel Live on Thursday night.

Mayer gushed about their duet Who You Love and talked about the song, which eventually landed on his new record Paradise Valley. As far as working in the studio with Perry, Mayer said, "She was fantastic, it was a really great experience."

Mayer elaborated on the duet, admitting he thinks it sounds like a duet you'd hear on the radio in the '70s or '80s.

"I listened back to it and it's really convincing, and I watched it get made and I'm still kind of taken aback," he said.

Earlier this week, Perry couldn't stop gushing over her man in the latest issue of Billboard magazine.

"He literally is a genius, as is evident from his songwriting," the 28-year-old beauty said. "I always tell him, 'Darling, you know I'm going to have to give your mind to science after you've passed, because we're going to have to understand how all these sparks work.'"

Inside the mag, Perry also opened up about her upcoming album Prism (out Oct. 22), admitting she penned some deeply personal songs in the wake of her painful divorce from Russell Brand.

"All the songs are real-life moments," she explained. "I can only write autobiographically. I put all the evidence in the music. I tell my fans if they want to know the real truth about stuff, just listen to the songs."

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John Mayer, Katy Perry