PHOTOS: Joe Jonas Strips Down For GUESS Underwear Campaign

Someone has been hitting the gym!

DNCE's Joe Jonas is one of the stars of the new GUESS underwear campaign. 

Shot by photographer Yu Tsai, the pics show 27-year-old Jonas in various pairs of underwear -- including many shirtless shots that call attention to his oiled and shorn chest and washboard abs (and more).

For some images, Jonas poses with model Charlotte McKinney.

Yu Tsai / GUESS

Yu Tsai / GUESS

Jonas told E! that to prep for the photo shoot, he did a lot of boxing with a trainer. "It's been a fun shoot, and my first time doing [a campaign] in underwear, so it's pretty exciting.

"It can be a weird thing to be sitting there in your underwear being photographed, but overall I had a blast."

Yu Tsai / GUESS

Yu Tsai / GUESS

Yu Tsai / GUESS

Joe is the first Jonas brother to star in a sexy underwear campaign -- although younger brother Nick Jonas posed in Calvin Klein undies for a 2014 feature in Flaunt magazine.

On social media, fans are reacting to Joe's pics and pecs!

Adapted from an article at iHeartRadio