Watch Jack White Explain How Al Capone's Prison Band Inspired New Song

"Humoresque," from White's latest album 'Boarding House Reach,' was informed by Dvořák compositions Capone performed in Alcatraz

Jack White, on Thursday's 'Tonight Show,' talked about the unexpected inspiration of Al Capone and Czech composer Dvořák on his latest LP.

Jack White detailed on Thursday's Tonight Show how a "bizarre" find – handwritten Al Capone sheet music – evolved into the closing track on his latest LP, Board House Reach.

"I saw this auction that said 'handwritten sheet music by Al Capone in Alcatraz,'" White told Jimmy Fallon. "I thought, 'What could that possibly be?' It said 'Humoresque' written on it, and I was like, 'Did he write a song in Alcatraz?' And the description said, 'He was in a band in Alcatraz. He convinced the warden to buy the music equipment. The band was called the Rock Islanders, and Machine Gun Kelly was the drummer in the band.'"

White was fascinated by the discovery, so he bought the sheet music and took it to a recording session in New York. Since he can't read music, he recruited drummer Louis Cato and keyboardist Neil Evans to help decipher the arrangement. When a veteran office worker passed through to deliver coffee, she recognized the piece as Antonín Dvořák's 'Humoresques.' 

"We found out through research some that other lyricist wrote [the lyrics] in the Thirties," White said. "So apparently Al Capone remembered it in prison and wrote it out by hand for his band to play. It's a beautiful song for a murderer."

Earlier in the songwriter's Tonight Show interview, he previewed his upcoming performance spot on Saturday Night Live. "I heard [host John Mulaney] was an altar boy when he was a kid too, just like me, so I said, 'You should write a sketch where we're both altar boys.'"

White also discussed his recent children's book, We're Going to Be Friends,' based on the 2001 White Stripes song of the same name. And he managed to slip in some political commentary during that sidebar: "I'm working on a new one," he joked. "It's called Anybody Can Be President!'"