Viggo Mortensen and Mahershala Ali confided their fears to each other while filming Green Book to help build a strong working relationship.

In Peter Farrelly's road trip comedy-drama, The Lord of the Rings actor plays Tony, who is hired by renowned pianist Don Shirley, played by Mahershala, to serve as his driver and security as he goes on a tour of the Deep South in the 1960s.

The majority of the story follows Tony and Don's blossoming friendship, with them both learning things from one another, and Viggo admitted to The Hollywood Reporter that he and Mahershala bonded by sharing their concerns and fears.

"With Mahershala on Green Book, we told each other things about ourselves and our lives," Viggo said. "We opened up and said, 'Well, I am worried about this. I don't know if I can do this.' You allow yourself to be vulnerable and if someone else does that in return, you are starting to get somewhere.

"You can't have beautiful moments or have something great happen unless you are willing to make big mistakes. You have to be willing to make an a*s out of yourself."

Oscar-winning Moonlight actor Mahershala, who picked up the best Supporting Actor Golden Globe for Green Book, explained that they already had a solid launch pad for their working relationship after meeting at a Hollywood bash.

"We met about two years ago at a big luncheon with a bunch of amazing actors," he continued. "And we found ourselves tucked in a corner and we spoke for a while. That set the tone for us sitting at the table with a script. We got to communicate some of our concerns and fears."

Green Book, which also won Best Screenplay and Best Motion Picture - Musical or Comedy at the recent Globes, hits U.K. cinemas from 1 February (19).