The pop stars are joining forces for the Future Now trek this summer (16), and Nick, who has become known for his buff body in recent years, admits her dedication to exercising forces him to push himself a little harder to stay in tip-top condition, too.

"Demi is killing it right now with her fitness game," he told "She looks amazing."

The two pals are planning to hire a professional to help them maintain their fitness regimen on tour, so they can deliver their high-energy shows day after day and stay healthy.

"I think we're going to get a trainer and have someone out on the road with us," he continued. "But also, every night on stage is a workout."

Diabetic Nick, 23, reveals he makes time to hit the gym at least three times a week, with West Hollywood's Heart & Hustle trainer Gregg Miele putting him through his paces, but his strict diet and fitness programme doesn't stop him from having the occasional cheat day.

Confessing his guilty pleasure, the singer/actor, laughed, "Cake is really great!"

Nick and Demi will kick off their Future Now Tour on 24 June (16) in Sunrise, Florida, but one state which has since been crossed off the gig list is North Carolina.

They had been billed to make stops in Charlotte and Raleigh on 30 June (16) and 2 July (16), respectively, but on Monday (25Apr16), Demi announced they have since decided against performing in the state to protest the introduction of anti-LGBT (lesbian, gay, bisexual and transgender) House Bill 2 (HB2) legislation, known as the 'Bathroom Bill', which restricts the public toilets transgenders can use.

"After much thought and deliberation, Nick and I have decided to cancel our shows in Raleigh and Charlotte," Demi wrote in a statement issued to officials at media organisation GLAAD. "One of our goals for the Honda Civic Tour: Future Now has always been to create an atmosphere where every single attendee feels equal, included, and accepted for who they are."

She went on to describe the law as "extremely disappointing", and now Nick has offered up his thoughts on the matter, insisting it wasn't an easy choice for them to cancel the shows.

"It's a tough thing and what makes it more tough is I have family in North Carolina and friends there," Nick said. "On top of the disappointment I'm sure some fans felt, I've got personal disappointment."