Joe Jonas
Yu Tsai
January 24, 2017 01:36 PM

Joe Jonas is the new face of the Guess Men’s underwear line, and he looks the part in the very sexy campaign photos.

The DNCE frontman, 27, shaped up for the ads in just 14 weeks — but it took a lot of dedication and hard work.

To get toned, Jonas turned to the experts at L.A.’s Unbreakable Performance Center (Nick Jonas and Demi Lovato are also fans of the exclusive gym) who put him on a rigorous workout and diet program that included five different phases.

“Early on we wanted to add a little muscle, then after he got that muscle we wanted to shred him up more, and then bulk him up more, then shredded him more, and then we were cutting weight so his abs just became ridiculous,” Unbreakable Performance founder Jay Glazer tells PEOPLE.

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Jonas’ fitness regimen was focused on boxing, with weights used as a complement.

“His workouts were pretty intense!” says Glazer. “We’re very high-intensity and high-power. [Boxing] shreds his shoulders and his core — it’s one of the best things you could do to shred. The way you really shred up is by getting your heart rate to go up and down drastically.”

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Even when Jonas was touring, he was accompanied by different coaches to keep him on track — his main coach was one of the most decorated women boxing champs, but other coaches helped mix up the workouts.

“One was a Green Beret who put him through Green Beret workouts,” says Glazer. And when he wasn’t on tour, “in the gym, we had him doing two-a-days,” he says.

WATCH: DNCE Rocks the Citi Concert Series on NBC’s Today Show!

Jonas also stuck to a very strict, calorie-restricted diet that allowed specific amounts of carbs, fat and protein eaten at specific times of the day.

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“He was so incredibly committed,” says Glazer. “We trained him like one of our fighters, and he really treated himself as if he were a pro-ball quarterback or UFC champion.”

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