Nick Jonas' brothers kept calling him the ''Hulk'' after he gained 15 lbs.

The 21-year-old hunk piled on the pounds for his MMA fighter role in the new drama 'Kingdom' and he admits his siblings Kevin, 26, Joe, 24, and Frankie, 13, kept comparing him to the green fictional superhero.

Speaking to E! News, he said: ''I gained about 15 pounds of muscle for the role ... I really wanted to look like an animal who internalises a lot, but when he's in the cage and he's fighting that's when you see this kind of animalistic mentality that he has.

''[My brothers] were calling me the Hulk and they were poking fun at me a little bit.''

Nick has now lost over half of the weight he gained for the part, but is still working out a few times a week.

He explained: ''The bulky muscle guy was probably good for a month or two, but I feel better where I'm at now. I started to include more fun activities instead of just going to the gym all the time.

''So it's a ton of different sports that I play and traditional workout stuff. I work out with a great trainer and he has a great gym. We do sort of circuit training and strength and conditioning.''

Nick, who was diagnosed with Type 1 diabetes nine years ago, has also realised the importance of nutrition.

He added: ''I really got into living a really healthy lifestyle and physical fitness last year.

''I saw pretty quickly how it improved my health and the diabetes. I've stuck with it.''