Shawn Mendes has become the latest celebrity to wear nothing but his "Calvins" in an underwear campaign, and his fans have gone crazy over it on Twitter. Their passionate support for the "Treat You Better" singer caused Calvin Klein to become a trending topic in the United States on Saturday.

Photos circulating on social media reveal that the ads have started popping up at Calvin Klein stores. In the print ad, you can see Mendes kneeling in a room, wearing a pair of blue undies from the esteemed fashion brand, offering up a clear view of his chiseled six-pack. In a short video clip included in the campaign, we see him zipping up his pants and leaving a room. The ad also features a girl, who is also shown off wearing underwear.

Based on the reaction from his fans, it looks the campaign caught them by complete surprise, and many of them expressed desperation to get to the nearest Calvin Klein store to see the ads in person.

"I don't know what's happening," wrote one Twitter user, who runs a Shawn Mendes fan page. "Suddenly pictures of Shawn modeling in his underwear were thrown at us, but I'm not complaining. Everyone say thank you Calvin Klein!!!"

"Shawn's Calvin Klein campaign is all what's right in the world," another fan wrote.

As his IMDB page notes, Mendes has the now-defunct social media app Vine to thank for his huge popularity. He started posting videos on the platform back in 2013, which attracted hordes of eager fans to his account. According to Fortune, talent manager Andrew Gertler found his videos online and contacted his mother about developing her son's music career.

Mendes got a record deal from Island Records in 2014, and his first single, "Life of the Party," hit the market in June of that year. While it sold well, it did not get the amount of radio airplay that they wanted.

Gertler said that their main stumbling block was convincing people that Mendes was a serious artist and not just a social media phenomenon.

"The reality is, it wasn't easy to earn the respect of people," he said. "It was hard for people to buy into the concept of a young Viner that is a career artist."

Despite the song's middling success, Gertler stuck with Mendes. Soon the singer was headlining his own tours and opening for Taylor Swift on The 1989 World Tour. Their efforts paid off, and now, Mendes is a Grammy-nominated artist who receives lots of radio airplay and, of course, his very own Calvin Klein underwear campaign.