Modern royals such as the Duke and Duchess of Sussex will not feature in the Crown because there is not "enough distance" from their stories, said the creator of the TV hit, Peter Morgan.
The final two series of the Netflix drama will bring it into the 21st century but Morgan said he has "a 20-year rule" to allow for "perspective".
Imelda Staunton will replace Olivia Colman as the Queen and Lesley Manville will take over from Helena Bonham Carter as Princess Margaret in the fifth and sixth series.
Explaining why the series will not explore modern royal life, including Prince Andrew's involvement in the Jeffrey Epstein scandal and Meghan and Harry's decision to leave the UK, Morgan told The Hollywood Reporter: "I just think you get so much more interesting (with time).
"Meghan and Harry are in the middle of their journey, and I don't know what their journey is or how it will end.
"One wishes some happiness, but I'm much more comfortable writing about things that happened at least 20 years ago.
"I sort of have in my head a 20-year rule. That is enough time and enough distance to really understand something, to understand its role, to understand its position, to understand its relevance.
"Often things that appear absolutely wildly important today are instantly forgotten, and other things have a habit of sticking around and proving to be historically very relevant and long-lasting.
"I don't know where in the scheme of things Prince Andrew or indeed Meghan Markle or Harry will ever appear. We won't know, and you need time to stop something being journalistic.
"And so I don't want to write about them because to write about them would instantly make it journalistic. And there are plenty of journalists already writing about them.
"To be a dramatist, I think you need perspective and you need to also allow for the opportunity for metaphor.
"Once something has a metaphorical possibility, it can then become interesting.
"It's quite possible, for example, to tell the story of Harry and Meghan through analogy and metaphor, if that's what you want to do.
"Because there've been so many examples in the past, whether it's Wallis Simpson or Edward VII, or whether it's Diana and Prince Charles.
"There have been plenty of opportunities in the past where there have been marital complications.
"There've been wives that have been married into the royal family that have felt unwelcome and that they don't fit in. So there are plenty of stories to tell without telling the story of Harry and Meghan."
The fourth series of the Crown is due to be shown at the end of this year.