Calvin Klein nearly broke the Internet on Tuesday, Jan. 6, when the designer featured Justin Bieber as the hunky new underwear model for the brand's notorious #MyCalvins campaign, reports Us Weekly.

The underwear ad campaign features Bieber with topless Dutch model, Lara Stone, who holds his crotch before he straddles her.

The "Amazing" singer, 20, had agreed to remain silent about his sexy photo shoot with Stone but now that the campaign is in full swing, he talked with Us Weekly about the project.

"I've wanted to be involved with Calvin Klein for a while now," the pop superstar told Us Weekly. "Earlier this year, I put up a picture on Instagram of me in their boxer briefs with the #mycalvins tag, and people went crazy for it and it got their attention."

The secret photo shoot took over two days to complete. "It was actually two-and-a half because I got sick during the second day," Bieber said. "Behind the scenes, everything ran like clockwork -- we'd come in, do glam, and get right to shooting."

Although the campaign was to be kept a secret until its debut, Bieber and Stone dropped hints before the official release. His strip-down in 2014 at the Fashion Rocks presentation was a clue, Bieber said, and, although the stunt incited boos from the audience, he wasn't worried about the crowd's negative reaction.

How does Bieber maintain those eye-popping abs and pecs? "I work out with my trainer, Patrick Nilsson, five days a week for about 45 minutes each," he said. "We do three days splits: back and triceps one day, chest and biceps on day two, shoulder and legs on day three, and abs every other day."

Other than an exercise routine, there was no special preparation for the shoot, according to the Biebs. "I do eat unhealthy sometimes -- I am a 20-year-old guy!" he said.