Assassin's Creed director Justin Kurzel says he was "pinching himself the whole time" as he couldn't believe Brendan Gleeson was starring in one of his movies.

Gleeson plays Michael Fassbender's on-screen father in the video game adaptation, and Kurzel - who previously worked with Fassbender on 2015's Macbeth - said it was "a real joy" to watch the pair at work.

"It's pretty amazing [to work with Gleeson and Fassbender], you're pinching yourself the whole time," Kurzel told RTÉ Entertainment.

"Maybe because I'd worked with Michael over a longer period of time but I'd kind of gotten used to his brilliance, but to see him work with Brendan - I've been a huge fan of Brendan's, I kind of had to constantly pinch myself that he was in the film and he was playing Michael's father, and the two of them had such a great camaraderie - it was a real joy to shoot that."

Gleeson and Fassbender will also play on-screen father and son in the upcoming release Trespass Against Us, and German-Irish actor Fassbender told us it was "a real treat" to star alongside Gleeson again.

Watch our interview with Michael Fassbender here:

"Brendan and I got on great on Trespass [Against Us] and I've been a fan of his since I saw him in Juno and the Paycock when I was 16, so it's one of those nice moments in this job for sure when you get to do that," Fassbender told RTÉ Entertainment in an exclusive interview.

The Kerry man recalled watching 1991's The Treaty with his grandfather, with the pair particularly enjoying Gleeson's turn as Michael Collins.

"He was a massive influence. I remember taping The Treaty for my grandfather at the time and we both agreed he was the best representation of Michael Collins," Fassbender said.

Assassin's Creed hits cinemas on January 1, 2017.

See our interview with Assassin's Creed star Marion Cotillar, and director Justin Kurzel here: