Jason Aldean's upcoming album, They Don't Know, is set to drop on Sept. 9, and he'll be joined on one of the album's tracks by an unexpected guest: Kelsea Ballerini.

Ballerini is a relatively new name to country music, although she has quickly skyrocketed to success: Her first two singles, "Love Me Like You Mean It" and "Dibs," hit No. 1, and her current single, "Peter Pan," is also enjoying chart success. But despite her success and growing name recognition, a duet with an established artist like Aldean may come as a surprise to some.

The song the two perform together is called "First Time Again;" it's the seventh track on They Don't Know. Aldean says in an interview with iHeartRadio that the song "was actually something I was going to cut on my own; we really didn't have a plan for it to be a duet." However, "the more we kind of got to listening to it, we thought it could probably set up that way, so we started thinking about people, you know ... and Kelsea's one of those who's off to a great start. She's really early in her career, first album, but she's off to a really great start, having some big songs, and, you know, I love her voice, I think she's got a great voice."

Fans can hear "First Time Again," along with the rest of They Don't Know, on Sept. 9. The album is available for pre-order on iTunes now.

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