If you loved the young dancer he played in “Billy Elliot” and his Bernie Taupin in “Rocketman,” you’re in for a shock when you see Jamie Bell’s latest film, “Skin,” out Friday. Based on true events, he plays a neo-Nazi, with a shaved head and a faceful of scary tattoos.

Not surprisingly, there weren’t a lot of laughs during that Kingston, NY, shoot.

“I wouldn’t say we had fun making this film,” the 33-year-old British actor tells The Post. “We got through it. And we knew that we had a duty and obligation to do it as honestly as possible.”

Bell plays Bryon Widner, the real-life founder of an Indiana white supremacist group who, after becoming a husband and stepfather, changed his ways, became a government witness and, over a painful two years, removed all his offensive tattoos.

To get into his mindset, Bell sat down with him.

“We talked a lot,” Bell says of meeting Widner, who’s currently in a witness-protection program. “I wanted to know what his life was like as a kid, and I wanted to know what his life was like before he enrolled himself in this group.”

‘I wouldn’t say we had fun making this film. We got through it.’

He says Widner told him that as a young boy he had no role model, was desperate to be accepted and was intensely insecure. That cocktail of extreme feelings led him to join racist organizations by age 14. Today, Bell says, Widner looks like an average guy.

“What I experienced when I was there: family man, extremely articulate, but also intensely paranoid and dealing with a lot of guilt and a lifetime of reckoning,” he says.

Physically transforming into Widner at his worst took daily applications of freaky fake tattoos — 14 on his face, 39 on his body — representing the different groups he’d joined and the specific crimes he’d committed. Bell noticed that once the temporary ink was on, people acted different around him.

“When I was wearing that stuff, I’d be out and about in public and people often don’t want to acknowledge the monster sitting next to them,” he says. “And I totally get it. I would probably do the same thing.”

At one point, the production ran out of money for the elaborate inking, and Bell was forced to keep the tats on his face for several days.

“They were like, ‘You can’t take them off. You’re going to have to keep them on,’ ” he says. “None of the crew wanted to hang out with me. I was eating alone.”

But as monstrous as Bell looked, the sweet-tempered actor tried to keep the three kids who play his girlfriend Julie’s children — she’s played by “Patti Cake$” star Danielle Macdonald — content and happy.

“I was a kid actor, too,” says Bell, who was 13 when cast as Billy Elliot. “I know what it’s like being around intense scenes and how they can make you feel. Suddenly, the line between acting and reality can feel very blurred. I was always trying to lighten the mood.”

It helped, he says, that his character had a dog, a sweet Rottweiler named Boss.

“The kids loved the dog,” Bell says. “The dog looks ferocious, but is actually incredibly tame.”

But who was there to make sure Bell himself was OK portraying such an angry, repellent character? He credits his wife, actress Kate Mara.

“I got home when production was done and my wife was there,” he says. “And she was, like, ‘Can you just go walk it off?’ ”

“I was completely unaware of it, but she was, like, ‘You need to calm the f - - k down.’ ”