People were pretty shocked to see James McAvoy, the skinny, boyish looking actor from Pride and Prejudice, absolutely jacked while walking around on set of his upcoming movie Glass.
The Scottish actor certainly has beefed up for the role, where he plays Kevin Wendell Crumb aka The Horde, a man with 24 different personalities including one called The Beast.
But he didn't get to become this rager of a character by doing a bicep curl or two; it involved a pretty intense workout and diet regime.
McAvoy's personal trainer Magnus Lygdback has told British GQ: "We had a lot of work to do. The Beast is supposed to be able to flex his veins and muscles and have a freaky look. It was about building as much mass as possible in a short time.
"I like to start the day with working out, because that's when you have the most energy. We had a program with which you go really hard on a couple of muscle groups at a time and then let them rest.
James McAvoy has certainly pounded on the muscle for this role. Credit: Universal Pictures
"So we would do legs one day, back and outside shoulders the second day, the third day the chest, front shoulders and core, and the fourth day, arms.
"That allows the muscles to recover before you work them again and also means you can do more sets, more reps on each muscle."
Glass is the final film in trilogy that ties in with Unbreakable and Split by M. Night Shyamalan. McAvoy's character entered the series in the second film, but Lygdback says James could have been much bigger then, and that's why he was called.
When it came down to what McAvoy put in his gob, Magnus had this to say: "I've never counted calories, because you can eat a bag of crisps and get 1,000 calories or eat a chicken breast and get 1,000 calories.
"It's about the quality, the proportion of the macros: fat and carbs are the energy source and protein is the building stone of the muscles and tissue."
Ah, so that's the secret.
McAvoy was hit with news headlines that he was woofing down 6,000 calories a day to get stacked, an accusation he denied. But he did admit to eating a hell of a lot.
He told Mr Porter last year: "He said: "I googled 'good way to put on muscle quick', just went into a gym and did it myself: a powerlifting routine called 5x5.
"You do five different exercises four or five times a week, and they're huge, big exercises. It's super-simple, but it works every muscle.
"Instead of eating two eggs in the morning, I'd eat eight. Then a snack of chicken breast. Then two chicken breasts for lunch, and then a steak or another snack. Then two salmon steaks for dinner."
Glass is out January 19 and also stars Bruce Willis, Samuel L Jackson and Sarah Paulson.
Featured Image Credit: Focus Pictures/Universal