'It was a relief to be normal and not have to look like a superhero'
Chadwick Boseman's Black Panther had met a sticky end when Joe and Anthony Russo, the directors of Avengers: Infinity War, made him an offer.
"It was after the premiere and I had actually just died on screen," Boseman says, as he leans forward in his chair.
"Joe and Anthony basically came to me, pulled me away from Robert Downey Jr and said, 'We gotta come and talk to you'.
"They were like, 'We have a script and we feel like you're perfect for it - and this is not a consolation because we just killed you, because you're coming back'."
The duo were true to their word, Black Panther was revived in Avengers: Endgame, and the script that the brothers handed to him was for the thriller 21 Bridges, on which they serve as producers, and he plays an NYPD detective.
It follows Andre Davis as he leads a city-wide manhunt for a pair of drug thieves (played by Stephan James and Taylor Kitsch) who just killed eight police officers after they interrupted their heist.
The story unfolds over the course of one night, as Davis directs the authorities to shut down all the routes off the island of Manhattan, including its 21 bridges, in a bid to find the killers.
It's a very different role to the superhero one that made him a megastar - following leading roles in films such as 42, Get On Up and Marshall - as the line between who are the good guys and who are the bad guys becomes increasingly blurry.
"There are no tricks here. There's no tricks to him. You've got to do all that running," Boseman says with a laugh.
"Stephan and I were r-u-n-n-i-n-g. I think it was more grounded, I think the preparation is different, whereas when you're playing Panther, there's a lot of choreography that you're practising over a long period of time. This is more like just being ready, so I didn't have to train like a professional athlete, I just had to be in shape, which is more normal."
While Black Panther requires him to look, well, superhuman, playing a sleep-deprived cop felt more achievable for the 41-year-old.
"It was just 'Get up and run' or 'Get up and ride the bike' - actually stay away from lifting too many weights.
"Because I didn't want to look like a superhero; if I look like a superhero, that's going to take away from the movie.
"It was trying to be a little more normal in how you do everything. It's a relief!"
But even so, the preparation wasn't all roses.
"You don't have to workout five or six hours a day, you don't have to do that, but there's a stress that firearms training puts on your body, because it's one-sided.
"So I felt all of this stress on my right side, stress in my back, and you're constantly trying to calm that."
In fact, his firearms training saw him firing 500 rounds at a time, with a powerful kickback at each one.
"You feel it as you hold focus, so you understand that tension the person has."
But the pain in his shoulders and back was nothing compared to the sleep deprivation that goes hand-in-hand with a film set entirely over the course of one night.
"The worst part is staying up all night, as we were doing night shoots.
"It's the same thing these officers have to deal with, they're up for three nights in a row and they're a little punchy but they're receiving information and having to race to a place and be completely armed.
"We were experiencing a similar thing, because we were up for a month and a half on night shoots and you're waiting and waiting, and then suddenly it's, 'Now shoot', 'Now run down the street'."
It's significant that Boseman serves as a producer on the film, which was helmed by Luther and Game Of Thrones director Brian Kirk, which gave him more influence on set and even a say in casting Sienna Miller as his on-screen police partner.
"You don't necessarily have to be able to produce to do this, but it's helpful as a leading man, because you're guiding the audience through the movie.
"You're telling them, 'Look this way' or 'Don't look this way', and so having a say in how that's happening, what takes are used... If I'm not producing, I might not see the first cut; I might not see the director's cut.
"As an actor, you're protecting your performance, always.
"Every actor, whether they know it or not, they should be protecting their performance, and so there is a personal thing of being able to go, 'Look, you're missing something here', or 'You missed what I did in this take over here because you cut that out - you missed this moment' and being a producer, you have access to be able to say, 'Take 3' as opposed to 'Take 4'.
"I think you have to be responsible; there's a great responsibility when you're acting and producing that you don't overuse that power.
"In this case, this movie is about the cast. This movie is all about who's my partner? Who is this woman? Sienna was perfect and as a producer, I was able to affect her being cast."
He already has a few other films in the can, but before he knows it, Boseman will be back in the gym, getting ready to slip back into Black Panther's vibranium suit for the eagerly awaited sequel, due for release in 2022.
"I think it's going to be a gradual thing," he says, as he mulls all the weight-lifting that lies ahead of him.
"So if I shoot two, maybe three things between now and then, I will probably start on the second one.
"Let me gain five or 10 pounds here and there, let me workout one extra hour this week, build up to it, change my weight gradually.
"Because the last thing you want to do, is do it all at once - it's unhealthy.
"If you put it off, you've got to do it all at once, and that's murder."
21 Bridges is in cinemas tomorrow