Billie Joe Armstrong, Norah Jones in sync on 'Foreverly'

• Green Day frontman has been a fan of the Everlys since childhood
• The batch of cowboy country and traditional folk tunes qualified as an oddity back in 1958%2C when the brothers recorded it
• %22We didn%27t tell anybody we were making this record%2C%22 Billie Joe Armstrong says

The typical label executive might not have foreseen harmony in a medley of Green Day's Billie Joe Armstrong, jazz-pop singer Norah Jones and a vintage Everly Brothers album of cowboy laments and dusky folk tunes.

That's why Armstrong and Jones, as Billie Joe + Norah, recorded Everlys homage Foreverly, out this week, under the radar.

"We didn't tell anybody we were making this record," Armstrong says. "We didn't tell our label. Our management barely knew. We were just a couple of friends playing music together."

The Everlys' Songs Our Daddy Taught Us, a dozen traditional tunes (Roving Gambler, Barbara Allen) and roots ballads popularized by Gene Autry, Tex Ritter and Charlie Monroe, was considered bold, even foolhardy, when the duo released it in 1958 on the heels of its rock 'n' roll breakthrough debut.

When Armstrong, an Everlys fan since childhood, heard the disc a few years ago, "I fell in love with it," he says. "I had only been aware of the more obvious stuff, the hits. What a cool record. I thought it would be cool to redo the songs but with a woman instead of copying what the Everlys did."

Jones, whom he'd met 10 years earlier at the Grammy Awards, was ending her fifth world tour when he called her last year.

"I was road-weary, and I didn't want to commit to a whole album," she says. "I was a little cautious. He was so excited and open. We decided to jump in and see how our voices gelled. Those harmonies are so important, and I wasn't sure we had it. I Googled enough YouTube clips of Billie Joe, and he definitely has that Buddy Holly rockabilly thing."

The harmonies and chemistry meshed instantly, and the two completed Foreverly in nine days at the Magic Shop in New York with Armstrong's engineer, Chris Dugan, and a small ensemble selected by Jones.

"He was loose, I was loose," Jones says. "We have a similar work ethic. I told him I didn't want to work super-long days. I've never made a whole album with someone I wasn't already good friends with. I got to know him a lot better. Billie Joe is a super-fun person. A side project like this was even more fun than doing my own thing."

Armstrong found the project irresistible.

The Everly harmonies "are so immaculate," he says. "And that record was pretty daring at the time. A lot of other rock guys were trying to go pop. Chuck Berry had a string of big hits, and the same with Jerry Lee Lewis and Elvis. And here the Everlys were playing these torch songs and murder ballads. For them to do something so dark and angelic was appealing to me."

He doesn't know if Don and Phil Everly, 76 and 74, respectively, are aware of Foreverly, but he's proud of the remake, even if some Green Day fans are irked and befuddled.

"I don't care what anybody thinks," he says. "I want to get weird, I guess. The great thing about this record is that it's all about tradition. Songs were handed down to the Everly Brothers. It was handed down to us. Who knows who will pick this record up years from now?"