The father and son actors had previously appeared in two of the same movies, but had never shared any scenes, so Kiefer had been searching for years for the perfect project for them both.

At one point, he realised he was running out of time due to his father's age, so he spoke to his screenwriter pal, who penned the script for the Western.

Kiefer admits the 2013 shoot was the longest time they have ever spent together as Donald was away working during Kiefer's childhood and they both pursued busy acting careers.

"I waited 30 years to make this film and expecting (sic) it to be life-changing," he tells Britain's The Independent newspaper, "It wasn't until the last few days that I realised this is the most time I've spent with my father... It was a little late, but I got to make a movie with my dad. It was the coolest thing ever."

He recalls being jealous of actors who used to spend more time with his father, including Timothy Hutton, who played Donald's onscreen son in 1980 drama Ordinary People.

Kiefer adds, "I walked up to Timothy Hutton when I was about 22 and said, 'You stole that moment from me and my dad. I didn't grow up with my dad and I wanted that moment with my father'. Timothy looked at me and said, 'I have got to buy you a drink now'."

Kiefer has previously recalled his nerves before the production began, saying, "When we started rehearsals, for the first two weeks, we were very professional... Then, the night before we started shooting, I phoned him (Donald) up and I said, 'You know, I just want you to know if tomorrow's a little awkward, it's because I'm really nervous', and he started to laugh and I think he said something to the effect of, 'Oh my God, I've already crapped myself'."