Green Day frontman Billie Joe Armstrong has usually kept quiet about his youth spent singing show tunes, but now that the punk rocker is opening the new musical "American Idiot" on Broadway, it's kind of hard to avoid.
"I didn't want to tell anybody I actually did that stuff—in punk rock maybe it seemed too much like I was a trained person, where punk is so about three chords and the truth or whatever," says Mr. Armstrong, 38 years old, who collaborated on "American Idiot," which opens April 20. The show is inspired by the band's hit rock-opera record of the same name and includes all the songs from that album.
From ages 4 to 14, Mr. Armstrong performed standards with a group of kids at veterans' hospitals, convalescent centers and other venues around Oakland, Calif. "He did things like 'New York, New York' and Liza Minnelli stuff, Frank Sinatra tunes, Broadway show stuff," says his former singing teacher, Marie-Louise Fiatarone. When he first entered the music school with his mother, Ms. Fiatarone recalls her late husband spotting the boy's blond curls and saying: "He looks just like Shirley Temple. I wonder if he can sing."