Hero Fiennes Tiffin Reveals “Ungentlemanly Warfare” Cast's Group Chat Name: 'I Gelled with All the Guys' (Exclusive)

Henry Cavill, Henry Golding, Alex Pettyfer and Alan Ritchson also star in 'The Ministry of Ungentlemanly Warfare'

Hero Fiennes Tiffin was ticking things off his career bucket list left and right while working on The Ministry of Ungentlemanly Warfare.

The British actor plays expert sailor and Irishman Henry Hayes in the Guy Ritchie World War II film, alongside an ensemble of stars: Henry Cavill, Alex Pettyfer, Henry Golding and Alan Ritchson.

While the actors were exploring all kinds of "ungentlemanly" war strategies in the film, Fiennes Tiffin tells PEOPLE they "all got on really well" behind the scenes.

"I feel like I gelled with all the guys," the actor, 26, says, noting that "the credit definitely goes to Alex Pettfyer, because he was the one who made the group chat, called the Scriptless Heroes."

That name is "a joke on the fact that Guy likes to often be quite spontaneous with his dialogue changes," he explains, before clarifying: "I have to add in there that every single time Guy changes something to the script, it makes it better. It's undoubtedly better. I don't know how he does it. He really is a genius."

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The guys went for a meal a few days before filming started, and though Ritchson, 41, "came on a bit later," he "slipped into the crew seamlessly."

"It was really nice. I'm the youngest on set, so it felt like they looked after me, and they did the organizing and the welcoming," Fiennes Tiffin recalls. "It was a really, really nice, fun, well-looked-after kind of situation for me on that one."

The After star says he formed the closest bond with Cavill, 41, with whom he had the most scenes.

"I really, really admire Henry and how he goes about his work and how he is as a person," he says. "He is really — a gentleman is the perfect word. I know it's ironic, because of the title of the movie, but Henry Cavill, I really aspire to behave like he does and have a career like he does."

When filming wrapped on the action-comedy last year, Cavill praised all of his costars in an Instagram tribute, calling Fiennes Tiffin a "mega star in the making."

"I was going to make a joke and say I paid him to say that, but I was so touched when I read that. It meant the world to me," he says, adding that it was "so kind of him to write that, and I learned a lot from him."

Related: Cary Elwes Reveals His Family Connection to Ungentlemanly Warfare: 'This Is a Deeply Personal Project' (Exclusive)

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Working with such an impressive group of actors — the cast also included Eiza González and Cary Elwes — was just one of the highlights for Fiennes Tiffin, who says it "was always a dream for me to work with Guy."

"I was joking to my friends: 'I've peaked, what do I do now? I've worked in a war movie with Guy Ritchie and Henry Cavill and all the rest of the great cast.' I was joking, but that is really bucket-list stuff," he says of the film. "There are not many roles that you could describe to me that would top that."

His love of the director dates back years. "When I was just starting out as an actor, your agents ask you for lists of your favorite directors and actors and people so they can get an idea of the kind of roles that are going to be your favorite and that you want to do. Guy Ritchie was the top of every director's list I'd write down."

The Ministry of Ungentlemanly Warfare is now available on digital and will be on 4K UHD, Blu-ray and DVD June 25.

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