“She’s a bitch,” says Charlize Theron, describing her latest screen creation, a Cold War secret agent with incredible fighting skills.

Undoubtedly one of the most talented actresses of her generation, from her Oscar-winning performance in Monster to her kick-ass role in Mad Max: Fury Road and her evil Ravenna in Snow White and the Huntsman, we always knew Theron wasn’t a woman to mess with.

But in case of any doubt, look no further than her upcoming film, Atomic Blonde. She plays the ultimate weapon in David Leitch’s groundbreaking thriller, and not just a double agent but possibly a triple agent.

Layered with so many fight scenes, it’s little wonder Theron walked away from the set worse for wear, revealing how she is undergoing her fourth root canal surgery tomorrow. “I chipped my tooth making this movie. Thanks David,” she deadpans.

Co-starring James McAvoy (playing just one character this time round) and Sofia Boutella (The Mummy), Theron’s MI6 Agent Lorraine Broughton is sent to Berlin during the Cold War to investigate the murder of a fellow agent amidst intrigue involving the KGB and CIA.

Theron was so passionate about Atomic Blonde, she also serves as producer on the film, which she has been developing for five years. “I’ve definitely been interested in the genre and exploring it as a woman, so we, as a company, have definitely been looking for things like this. My company got sent an unpublished graphic novel from Oni Press called The Coldest City – it was really just an outline, but there was something about it that really grabbed me. So we met with [screenwriter] Kurt Johnstad and he did a spec for us,” says Theron, who surprised audiences at CinemaCon with a sneak peek at Atomic Blonde.

“It’s a spy action thriller with lots of cool shit,” she adds. “My character gets called into Berlin just before the wall comes down and she gets dragged into double agents, triple agents, and this rogue world where all these spies have gone completely feral. It’s a really colourful world.”

It’s a big action year for Theron, having also joined the cast of The Fate of the Furious. Although she insists she has very little action in that franchise, and that her menace comes from within.

The actress is joined by David Leitch, who says: “This type of genre movie isn’t right for everyone and it’s not right until you have the people who can pull it off –an actor who is prepared to go through all the training and give 110 per cent, get the crap beaten out of her, and still keep coming back.”

Almost in homage to Jason Bourne, Atomic Blonde showcases Theron as a mean, lean, fighting machine in raw and bloody fight sequences. “We really wanted to show that it hurts to get in a fight. There are a lot of action films where people are taking hits and getting right back up. That’s not what we do,” she explains.

Theron describes her training for the role as hard work. “I’m proud to be 41 years old, but there was nothing easy about it. For the first five weeks, I didn’t think we were going to be able to make this movie. It was tough. I had to learn martial arts and a real style of fighting and it also had to look real and it also had to look like my survival relied on it.

“I’m a tall girl and I can look like Big Bird really easily! But I took this stuff really seriously and knew it was only going to work if I got this stuff down. So it was three months of three hours a day of intense training – and there were days that I just could not get out of bed.”

Having helmed John Wick and now in production on Deadpool 2, Atomic Blonde is totally in Leitch’s wheelhouse. With a hard R-rating, the former stuntman-turned-director doesn’t skimp on the sex or violence. Theron’s steamy sex scene with co-star Sofia Boutella has already created enormous Internet buzz, and when they attended a Focus features luncheon at CinemaCon, the pair held hands on stage.

Boutella, who’s also having a great year between The Mummy and Atomic Blonde, plays a mysterious French agent who becomes entangled with Theron.

“We made bold choices,” says Leitch. “We wanted the film to be provocative in a lot of ways, not just in our action style but also in our world, so we really went for it. We tried to turn the thriller on its head and have fun with it and create a world that’s punk rock and ballsy. Everything you want is on the other side of fear.”

“Making Atomic Blonde was a five year journey and we worked our balls off. I have no more balls – I’m all girl now,” adds Theron, who is 100 per cent girly today, dressed in a silk purple-flowered mini dress.

Talking about a recent sneak screening of the film at SXSW, she adds: “The audience just loved it and it’s the closest as I’ll ever get to feeling like Bono. It was like a rock concert.”

Atomic Blonde is in cinemas August 3.