John David Washington "couldn't believe" Sir Christopher Nolan wanted to cast him in 'Tenet'.

The 40-year-old actor - who is the son of 'Gladiator II' star Denzel Washington and his wife Pauletta - led the director's 2020 sci-fi/action flick, but he was so stunned to play the Protagonist, he was convinced the 54-year-old filmmaker would tell him it was all a prank once they started filming.

During an appearance on the 'Little Gold Men' podcast, John David said: "Ain't no way he wants me in this thing.

"Obviously, when you first get it, I couldn't believe it. And then once I started believing it, after day three, he didn't call me saying 'psych.' I was like, 'Alright, let me try to figure out this character.'"

'Tenet' - which also stars Robert Pattinson, Elizabeth Debicki, Kenneth Branagh and Aaron-Taylor Johnson - follows a former CIA agent who is recruited into a secret organisation and is tasked with finding the origin of objects that are able to travel back in time.

While he enjoyed working on the movie, Washington admitted he struggled to understand the plot of the film - even after it hit cinemas in 2020.

Speaking to GQ Hype about the movie, he said: "I mean, literally on the first read, I thought I understood it, strangely. In my delirium, I thought I totally had, and I realised as the day went on, 'Ah, I don't have it at all.' But to answer your question directly, I'm still kind of grasping it."

When he landed the role, the actor was "locked" away in 'The Dark Knight' filmmaker's office reading the script, which took an excruciatingly long time due to the complexity of the movie's story.

He said: "It took me about four hours. I'd read maybe 10 pages, go back five, read another 10, go back two ... I was playing classical music on my iPad to make me go slower, make me think I'm smarter. I tried everything - took my shoes and sweater off, did some stretches. I couldn't believe I was locked in his office reading this script nobody knows about."

While he struggled to wrap his head around the movie, the 'BlacKkKlansman' actor also revealed he wouldn't even tell his own father Denzel about the story of 'Tenet' out of fears the 'Oppenheimer' director was always watching over him.

He said: "I would love to [tell Denzel Washington], but I always feel he [Nolan] are looking at me. Like I've been bugged. Chris will know, it'll get out. I don't want to get waterboarded, so I always tell the truth, and I didn't say anything."

However, 'The Creator' star added he and his parents celebrated like he "won the World Cup" after finding out he had secured the role.

He said: "I was at my folks' place at the time, and we were just screaming at the top of our lungs, it was quite the spectacle. We were charging up and down the halls, flipping papers, anything we could get our hands on. We were so excited - it was like I won the World Cup."