Bieber's trainer: He's well-endowed!

[RoadWarrior]

Justin Bieber is 'well-endowed', according to his trainer.

The 20-year-old Baby recently singer stripped down for an underwear campaign with Calvin Klein, but it's been claimed this week that the images were altered to make his muscles and his crotch look bigger. Now Patrick Nilsson, the man responsible for curating the hitmaker's exercise routine, is claiming it's all Justin.

"I can definitely confirm that he is a well-endowed guy," Patrick told Access Hollywood.

The photo shoot features Justin looking beefy in nothing but a pair of the label's tight white trunks. Website BreatheHeavy.com claimed to have the original photos of the pop star in which he appears significantly less bulky, but Patrick says it's all natural ' even his private parts.

"I sound weird saying that, but yes," said the fitness guru.

Patrick also spoke with HollywoodLife.com this week, telling them Justin is on a muscle building spree. He declared his plans to add pounds to the singer's frame.

'Justin has put on 20 pounds of muscle and he's still working on it. It's a work in progress. We want to put on at least 15 more pounds - he's going to get even bigger. That's the plan,' he told the gossip website.

Justin frequently posts pictures of himself working out in the gym to his various social media profiles, showcasing his sweaty efforts.

He spoke about his regime last year, saying: 'I have been working out in the gym, getting bigger, trying to get sexy for the ladies.'

This latest Calvin Klein ad sees Justin pose alongside Dutch model Lara Stone, who appears topless in the images.