Emma Corrin's Princess Diana casting was like watching The X Factor, says The Crown star Josh O'Connor

Asked about the casting process for the role of Diana, Corrin said: "It was a very long process, it took about a year I think, actually. It was kind of quite stressful, and a lot of different stages, but in retrospect it all worked out brilliantly. At the time very stressful. Josh was actually there when I got offered the role, so he compares it to X Factor, which is probably quite accurate."

O'Connor added: "It was like X Factor."

Corrin also revealed that she initially felt daunted by researching the "iconic" role, especially given the "overwhelming" amount of information available about Princess Diana.

She explained: "It's a very iconic role, very daunting, I felt very overwhelmed to begin with. I wasn't quite sure how to embark on research because I found it quite overwhelming, there being so much out there, so much factual information about her that really didn't help me at all really understand where I was going with the character.

"But, you know, the brilliance of Peter [Morgan]'s writing is he creates these fictionalised versions of these characters, and when I was reading scripts I kind of finally realised, 'oh this is my version of Diana, this is a character I'm creating', and as an actor there's no greater thing thank when you have the freedom to create and play with a character. So it kind of helped me get over the inaccessibility, I suppose, that I found before."

Asked about whether the pair felt any on-screen chemistry, Corrin said: "We kind of knew each other roughly before because we have a - one of my best friends knows Josh very well and vice versa, we've got a mutual friend. So yeah, we knew each other.

"The first scene we acted in together, that was in Scotland, and we were in Scotland together and then we both flew to Spain to film in Spain for a month. So we got to know each other so well and it was so great, we were very similar I think."

Speaking to RadioTimes.com, O'Connor likened playing Charles to playing a Shakespearean villain, but stated that he still felt "very protective" over Charles.

O'Connor said: "Over the real Prince Charles, of course I do [feel protective], yeah. As I would with any human. But... I've long since let go of it being too much about a real person. I think it's pure melodrama, it's pure fiction, punctuated with real historical events.

"But I do feel protective over my character, I feel very protective, and obviously when you're playing - I remember there was a great bit of advice, I won't go on too long, but there was a great bit of advice that Pete Postlethwaite used to say about when you play a Shakespearean villain, you don't play them as a villain, you play them as a saint. Because everything that they say and everything they do, they believe to be saintly. The right thing to do.

"So yeah, when I'm shouting at Diana, in hindsight I look back and go, 'God, why can't he just be kinder? Why can't he see that she's struggling as much as he is?' – but at that moment he doesn't see it, so you have to believe it. So I do feel protective to a point, but not so far as it would compromise the story."

The Crown season four will be released on Sunday 15th November. Looking for something else to watch? Check out our guide to the best series on Netflix and best movies on Netflix, visit our TV Guide, or find out about upcoming new TV shows 2020.