Nick Jonas stripped down on the third-season premiere of "Running Wild with Bear Grylls."
Monday's episode showed the 23-year-old singer and host Bear Grylls crossing a freezing lake in the Sierra Nevada mountains in nothing but their underwear.
"Most of the lake is frozen over. There's no sugar-coating it. What's in store for Nick and me is pain," Grylls said. "He's got to really dig deep. Probably more than any other point of this journey."
"I'm freezing right now. My toes are freezing. But it's crazy what happens to your body, the instincts that kick in," Jonas reflected after the swim. "You just have to go, push yourself."
Grylls helped Jonas warm up his feet by sticking them under his armpits -- the "second warmest part of the body."
The singer is diagnosed with type 1 diabetes, which can cause circulation issues.
"Running Wild" sees Grylls, a British adventurer, take celebrities on 48-hour survival adventures in the wilderness.
Julianne Hough, Courteney Cox, Shaquille O'Neal, Lindsey Vonn and Vanessa Hudgens will also appear in Season 3.
"Ultimately, this show is about taking these stars on the adventure of a lifetime and being alongside them when they discover something new and empowering about themselves and their world," Grylls previously said in a statement.
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Jonas last released the solo album Last Year Was Complicated in June, which debuted at No. 2 on the Billboard 200.
He and longtime friend Demi Lovato are presently on their Future Now tour.