Justin Bieber showed off his buff body and six-pack abs in a new Instagram picture with his trainer Credit: Courtesy of Justin Bieber

Someone's been hitting the gym -- hard. Justin Bieber gave his millions of Beliebers quite a treat on Wednesday, Oct. 9, when he shared a shirtless picture of himself on Instagram.

The photo shows the 19-year-old pop star flexing his buff biceps and flaunting his six-pack abs in nothing but a pair of black pants and a baseball cap. He looks semi-stunned (perhaps by his own muscles?) and is pointing at a (fully clothed) man next to him. 

"Me and my trainer," Bieber captioned the shot.

The singer, currently on tour in Asia, most recently made headlines for his new song, "Heartbreaker," which he released on Monday, Oct. 7, as part of his Music Mondays stunt. (He plans to share a new track every Monday for 10 weeks.)

"These songs are different," he tweeted. "These are my journals." 

"Heartbreaker," in particular, seems to parallel the star's relationship with ex-girlfriend Selena Gomez. "It's a song for people going through heartbreak -- like I was when I wrote it," he said of the tune. "It means so much to me to be able to share what I was and still am going through, with my fans. I'm very proud of this song and I hope it gives my fans some insight into my heart."