Billy Joel returned to pop songwriting in 2007 with an unexpected surprise: a one-off protest song.

“Christmas in Fallujah,” which put a sad spin on the ideas and emotions found in John Lennon’s “Happy Xmas (War Is Over),” was only the second pop tune Joel had released since 1993’s River of Dreams. The single arrived as an iTunes exclusive, punctuated with fiery and tough anti-war rhetoric.

The topic and dark tone weren’t the only surprises. The biggest shock: Joel didn’t even sing on the song.

Instead, the Joel original featured 21-year-old unknown Cass Dillon, who would go on to play guitar with and date Joel’s daughter Alexa Ray. Dillon joined Joel onstage on Dec. 1, 2007, to debut “Christmas in Fallujah” in front of a packed house at Chicago’s Sears Centre. With the full power of Joel’s live band, Dillon blasted out the grunge- and “Kashmir”-influenced tune singing, “We came to bring these people freedom / We came to fight the infidel / There is no justice in the desert / Because there is no God in hell.”

Joel and Dillon invited soldiers to join them onstage for the song's debut. The troops shouted “oo-ra” along with the song’s refrain from behind the band. As with Lennon’s signature Christmas song, Joel and Dillon’s work confronted a war the American public had long soured on.

Listen to Billy Joel's 'Christmas in Fallujah'

Joel noted that a flood of letters he received from the U.S. forces fighting in Iraq inspired him to write the song. But after finishing the composition, the 58-year-old artist felt a young man should give voice to the lyrics.

“I didn't feel I was the person to sing this song,” he wrote on his website. “I thought it should be somebody young, about a soldier's age. I wanted to help somebody else's career. I've had plenty of hits. I've had plenty of airplay. I've had my time in the sun. I think it's time for somebody else, maybe, to benefit from my own experience.”

Joel's guitarist Tommy Byrnes discovered Dillon during a set at the Drama Cafe in Baldwin, N.Y. He was struggling to find fans as a college dropout trying to navigate the competitive singer-songwriter scene. Byrnes connected Dillon to Joel, and the pair clicked. Joel flew Dillon out to San Francisco to record “Christmas in Fallujah” on Veterans Day.

Proceeds from the song were donated to Homes for Our Troops, a nonprofit organization created to build specially designed homes for returning soldiers with severe disabilities. Nevertheless, Joel continued to struggle with the idea of a protest song.

“I never liked when a rock star got up onstage and told people how to vote,” he told Rolling Stone at the time. “I find it insulting. But I believe if an artist feels strongly about something, it should be reflected in their art. Ultimately, everything's political. Even love is political.”

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