Charlie Hunnam was the "biggest" he's ever been while shooting 'King Arthur: Legend of the Sword'.
The 37-year-old actor had to bulk up for his titular role in Guy Ritchie's upcoming medieval epic and though it was a tough regime, the British star made sure he still had "fun" with his workouts.
He said: "Over the six month period of shooting 'King Arthur: Legend of the Sword' my size fluctuated a little bit, but I actually got to be the biggest I've ever been on the film. I put on a good 20 pounds.
"It involved going to the gym, lifting weights, eating lots and lots of food, particularly protein, and repeating the process until your muscles are big and swollen.
"But I had fun with it. I mixed it up, did some boxing and, obviously, was very active learning sword fighting and stunts."
But Charlie was more interested in the transformation of his mental wellbeing than his physical shape as a result of the sessions.
He added to channel24.co.za: "But for me, the least interesting aspect of exercise is the physical effect.
"What's really exciting is the mental, psychological, emotional aspect of exercise.
"You feel a significant difference in how you feel in your day-to-day life when you stop working out."
One of Charlie's favourite things about working on the movie was saying in caravans close to the set with Guy and the rest of the cast.
He said: "Guy does have an exceptionally cozy trailer. It's very difficult to get him out once he's got the log fire going and some eggs cooking on the stove. Guy creates this dynamic wherever he goes.
"The camping was wonderful. I'd always dreamed about what it would be like to just live around a film set and not be taken out of it. This was that experience for a brief period of time. We were in Wales for three weeks, but we all lived together in these little caravans by a lake. Some of us would jump in the icy lake every morning at 06:00 for what we lovingly referred to as the Plunge of Death.
"Guy would come out of the cabin and start talking about the day's filming, and we'd have breakfast together and walk from our trailer onto the set. Before we knew it we were in the zone and doing our thing. It was a lovely way to make a film."