Justin Bieber fans were in for a special treat Wednesday. The 19-year-old heartthrob took to Instagram to share a yet another shirtless snapshot.

Wearing only pants and a baseball cap, Bieber, flexed his biceps as he showed off his chiseled chest and washboard abs. In the pic, Bieber points to his personal trainer, Patrick Nilsson, who stands grinning by his side. Judging by the Biebs stellar transformation, it's clear that two have been very busy lately. During an interview with Newsday, Nilsson, 29, revealed the details of his intense training regimen.

"His chest and shoulders - we need to build those up," Nilsson explained. "It's all about looks."

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The duo trains together for approximately 40 minutes each day, five days a week and if good "looks" were the objective, their hard work has paid off. Fans can say goodbye to the skinny, floppy-haired kid of yesteryear and hello to a new, improved Justin Bieber.

"I want him to look like Marky Mark," Nilsson joked "I feel like this is what he needs to get where he wants to be. He's definitely leaner and a lot stronger."

The "Heartbreak" vocalist echoed his trainer's sentiment adding, "Who doesn't like working out chest and biceps?"

As for Bieber's diet, Nilson revealed that the crooner can eat pretty much anything he wants.

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"It's more about making sure he eats," Nilsson told Newsday. "He's the only client I allow to have McDonald's whenever he wants. But he also likes chicken breast, whitefish, salmon, turkey, steak, rice, mashed and regular potatoes and weird greens like cauliflower."

Earlier this week, Bieber released his newest single "Heartbreaker," the first installment in the singer's "Music Mondays" series in which he will release a new song each week, for 10 straight weeks. He is currently traveling and performing on tour in Asia.