The boss has gone hillbilly!For the first time in his 50-year recording career, Jersey Shore rocker Bruce Springsteen has hit the country charts with a new duet with country superstar Zach Bryan.

Friends say it’s giving the 74-year-old “I’m on Fire” rocker a shot in the arm after he was forced to cancel a string of U.S. and European concert dates for lingering health problems.

“Bruce is a big country music fan — he’s been covering Hank Williams Sr. songs at his concerts for decades,” an insider exclusively tells Closer. “Still, he’s felt like he shouldn’t crash country music’s party by invading their territory.”

But when chart-topping singer-songwriter Bryan, 28, asked him to guest on his new single “Sandpaper,” Bruce couldn’t resist — and now the song is not only climbing the country charts, but the pop charts as well, making this Bruce’s first Top 100 hit in 15 years!

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“Bruce is a realist. He can still pack ’em in at concerts when his health allows, but he says people don’t want to hear new music from old farts like him,” the source continues. “He was astounded that Zach, 46 years younger, is a fan and wanted to duet with him. Bruce says he owes Zach a debt of gratitude for putting him back on the charts!”