The two play a father and son in the new western Forsaken. "Working with him is something I have wanted to do for 30 years," Kiefer tells PEOPLE.
The 24 star says because most of his father's films were R rated, he had to wait until he was 18 to see them. Then, in one weekend, he sat down and watched as many as he possibly could.
"I remember feeling really bad as a son that I wasn't aware of not only how prolific my father was as an actor but what he had really contributed to the art of cinema," says Kiefer.
For Donald, working with his son was a "terrific" experience and he tells PEOPLE Kiefer is a "wonderful actor."
Although they are now very close, Kiefer, who was raised by his mother Shirley Douglas after she and Donald divorced in 1970, admits his relationship with his father was strained when he was younger but adds most father and son relationships can be complicated.
"There is inevitably always going to be a point when the younger lion wants to take on the older lion and then there is always going to be a point when the older lion is going to need the younger lion to help."
The film, which also stars Demi Moore and is directed by 24 director Jon Cassar, is in theaters now.