Dominic West "didn't think it was appropriate" to ask Prince Harry for advice about 'The Crown'.
The 53-year-old actor portrays his friend's father, King Charles, in the fifth season of the Netflix regal drama but he didn't want to get in touch with the Duke of Sussex before he started filming.
He told 'Entertainment Tonight' at the premiere of the new series at London's Theatre Royal Drury Lane: "I didn't think it was appropriate to call him up and ask him for tips.
"I haven't spoken to him for many years."
Dominic first got to know Harry in 2013, when they both took part in the Walk With the Wounded charity race through Antarctica.
He said: "We did walk to the South Pole together with a lot of wounded soldiers, so I got to know him pretty well."
The former 'Affair' actor is an ambassador for the Prince's Trust - the charity founded by Charles in 1976 - and he felt it was important he notified the organisation when he accepted the role of the former Prince of Wales.
Asked about claimed he had offered to quit as ambassador, he said: "I just thought I would inform the Prince's Trust that I was playing the part. And I felt they had a right to know that. So, that's as far as it went.
"You can't really resign. It's not really a job."
Meanwhile, Dominic admitted it was "pretty frightening" taking over the role from Josh O'Connor, particularly because his co-star Elizabeth Debicki, who portrays Princess Diana, was so well prepared.
He said: "I remember the camera test and it was me and Elizabeth. We're doing a test together and she immediately -- it felt like it anyway -- it felt like she had everything in place already and we were a couple of months off starting and I felt I hadn't got anything.
"Also, of course, you feel in front of a crew that's been doing this for five years with two other casts and you think everyone's going, 'Dear,'" he continued, with a laugh. "So, it was pretty frightening."