Billy Joel has broken his self-imposed retirement from pop for the second time in a year, but he'd almost rather you didn't know that. The second new Joel-penned single since his last pop album, 1993'

Billy Joel has broken his self-imposed retirement from pop for the second time in a year, but he'd almost rather you didn't know that.

The second new Joel-penned single since his last pop album, 1993's "River of Dreams," is called "Christmas in Fallujah" and hits iTunes Dec. 4. There are two major differences between it and the classics that have made him one of the best-selling artists of all time. First, there's no piano on it, and second, there's barely any Billy Joel on it, either.

Instead, for what Joel says is a first, he's written a song expressly for another singer, a 21-year-old Long Island native named Cass Dillon. Joel tells Billboard the inspiration for "Fallujah" was partly born of letters he's received from service personnel overseas, but also simply from years of the realities of war.

The song came to him quickly, Joel says, as did the realization that he wasn't the guy to record it. "I thought someone with a young voice should be singing this, someone just starting out in life," he says. "Plus, you know, I'm 58 years old. My voice isn't the voice I was thinking of when I was writing; I was thinking of a soldier, someone of that age."

Enter Dillon, a young singer/songwriter who'd spent a few years under the wing of Tommy Byrnes, Joel's longtime musical director. Dillon left college two years ago to pursue a musical career, and has spent the intervening years on the coffee-shops-and-bars circuit. Byrnes had played Joel several of Dillon's songs, and when it came time to find a singer for "Fallujah," Joel says Dillon "popped right into my head."

Click here to watch Dillon on Billboard Underground.

For more on "Christmas in Fallujah," see the Dec. 8 issue of Billboard, on newsstands and online at Billboard.biz today (Nov. 30).