For British actor Sam Claflin, dying was not easy. His character suffers a gruesome end in The Hunger Games: Mockingjay Part 2, the final instalment in the popular dystopian saga, and it proved a physically taxing moment.

In fact, the scene proved so exhausting that the 29-year-old, who plays Finnick Odair, had to take on extra oxygen.

"It was a physically challenging day," he recalls of his death scene. "I had to be put on oxygen tanks because I was struggling to breathe at one point. I was so tired because the costume was weighing me down.

"They had put foam in my backpack to make it look padded out, but the foam was soaking up the water we were filming in, so I was carrying all this weight around. And the stunt guys were like, 'Do you want some assisted breathing?' I thought I would give it a go and it burnt my nostrils.

"That day of filming was, by a long shot, the hardest day at work I have ever, ever experienced."

Mockingjay Part 2 is Claflin's third outing in The Hunger Games films after his debut in the second movie, Catching Fire (2013). His character has undergone quite a journey, starting out as a potential nemesis for the series' heroine Katniss Everdeen, played by Jennifer Lawrence, as they prepared for gladiatorial combat.

"Initially, you meet Finnick and you think he is a bad guy. He is a bit arrogant, overconfident, physically charming and charismatic," says Claflin. "That Finnick was enjoyable to portray."

In the next film, Mockingjay Part 1, his character became "someone vulnerable, sensitive, broken, upset, worried, anxious and scared".

"For me, the role has been a real blessing. Rarely in franchise movies do you get to go on such a journey, especially with a supporting character."

Finnick might be a supporting character, but as a charming hunk, he has proved popular with fans. On screen, he is well built, sporting a physique that is a long way from Claflin's.

"For me, going to the gym is definitely hard work," Claflin says. "When I stop filming, I don't want to work. I don't go home in the evening and continue to work out - that is just silly. I am an Englishman, I like a beer and I like a burger.

"I definitely allowed myself some much-needed downtime after Catching Fire. I didn't have a personal trainer going into Mockingjay, which meant I had a lot of work to do to get back into Finnick's state."

Despite the time he needed to invest in the gym, the character has been a real boon for Claflin.

"Quite simply, this character has put my name on the map," he says. "I feel that without these films, I was carefully and slowly climbing the rungs, but this has propelled my career and given me an audience who are loyal and respectful.

"Initially, a lot of people were nervous about me being cast in the film and fans of the book were nervous that I was going to mess things up for them.

"But I think that they have come round and that has made me grow as a person and grow in confidence."

The resulting fame he has enjoyed, he says, can be strange. His privacy is compromised more in the United States than in Britain.

"I went to The Hunger Games exhibition in New York recently," he says. "We walked around and there were fans and families looking around. The first five or 10 minutes, I went totally unnoticed."

Suddenly, however, a person noticed him. "And then everyone noticed. It was a ripple effect. But it was nice to know that I made that experience for fans there that day - at The Hunger Games exhibition, they met Finnick Odair."

Back home in London, England, where he lives with his wife, actress Laura Haddock, his anonymity is more assured.

"I don't go out during the day much, unless I am going to the gym, which is a different audience," he explains. "A lot of female fans of The Hunger Games films are under 16 and won't be at the gym.

"If I go out at night, I will be in a pub and the girls would be underage, so they wouldn't be in there. Funnily enough, at the Glastonbury festival this summer, more men noticed me, saying, 'My wife's a big fan.'"

It could have all been very different had Claflin, who was in the Norwich City youth football team, not suffered a broken ankle in his mid-teens.

"At the age of 15 or 16, I broke my ankle. Before that, I was playing football six nights a week, and then suddenly I couldn't do that any more because my leg was in plaster. I needed something to do so I threw myself into drama," he recalls.

He made his film debut playing the devout missionary Philip Swift in 2011's Pirates Of The Caribbean: On Stranger Tides. He followed that with another supporting role in another big studio picture, playing William in Snow White & The Huntsman (2012).

After he appeared in Catching Fire, however, he secured a number of lead roles, first in supernatural horror film The Quiet Ones (2014) and then in the romantic drama Love, Rosie (2014).

"Thanks to The Hunger Games, opportunities have come up that would not have come up otherwise," he says. "I have had the opportunity to meet directors who wouldn't have wanted to see me."

Next, he will be seen alongside Game Of Thrones star Emilia Clarke in Me Before You, the big-screen adaptation of author Jojo Moyes' romantic novel. He plays a quadriplegic in the film.

"It has opened my eyes to a new world," he says. "It allowed me to look at life differently and to not take things for granted."

Every character he plays unlocks a key to something in him, he says, and "I become a different person".

"Pirates Of The Caribbean was the one that made me go, 'This is what filming is like.' And I have grown from that and will continue to grow, hopefully, in the right direction.

"I still have a long way to go before I am completely happy. I see someone like Eddie Redmayne or Robert Pattinson and a lot of people will agree with me that they are better actors and better looking. I have a long way to go before I am walking into the rooms they are in, but I like a challenge."

•The Hunger Games: Mockingjay Part 2 opens in Singapore tomorrow.

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