Justin Bieber Pumps Iron in the Gym, Stares at Amber Rose's Cleavage—See His New Instagram Pics!

Singer wears only a towel as his manager Scooter Braun hits the steam room

Remember when Justin Bieber was a scrawny lil' thing?

Those days are long gone. The tattooed troublemaker shared a photo collage via Instagram Thursday. The pictures show pop star doing bicep curls with 40-lb. weights in addition to doing stomach crunches to keep his six-pack poppin'. "Back in the gym #dontbescared #orangegymrats," he wrote in the caption.

Earlier that day, the 21-year-old "Confident" singer tweeted, "Push yourself to be great." Indeed he did!

After pumping iron, the Canadian crooner hit the showers; Scooter Braun shared an Instagram video of the singer wearing only a towel. "That steam room was fantastic," Bieber's fully-clothed manager joked.

Later that night, Bieber partied with a few famous pals in L.A. He posted an Instagram picture of himself hanging out with Amber Rose, and although he's wearing sunglasses, it appears he's staring at the model's cleavage! "Good night with friends," he wrote in the caption.

Rose shared a similar snapshot via her Instagram account, writing, "The Biebs @justinbieber wanted a pic with Muva and I him. He's a sweetie pie." In the pic, Rose and Bieber pose together at a different point in the night at Riviera 31 at the Sofitel.