Season four, which is based on real-life events but not entirely factual, premiered on Netflix on Sunday with a range of new characters, including Princess Diana and then-prime minister Margaret Thatcher.

In the first episode of the new series, Lord Louis Mountbatten, played by Charles Dance, confronts his great-nephew, Prince Charles, for being romantically involved with Camilla, who was married to Andrew Parker Bowles at the time.

In the series, Mountbatten is also shown to write a letter accusing Charles, portrayed by Josh O'Connor, of contemplating such "ruin and disappointment" to himself and his family, and orders him to instead marry "some sweet and innocent well-tempered girl with no past."

In the show, Charles receives the correspondence after learning that Mountbatten has been assassinated by the IRA -- but some critics insist there is no evidence that such a letter was ever written.

Writer Morgan addressed the show's portrayal of the interaction in an episode of "The Crown" podcast, explaining that, while he "made up" the scene, he believed that the fictionalized interaction would have aligned with Mountbatten's views.

"I made up in my head -- whether it's right or wrong -- what we know is that Mountbatten was really responsible for taking Charles to one side at precisely this point and saying, 'Look, you know, enough already with playing the field. It's time you got married and it's time you provided an heir,'" Morgan said.

"I think everything that's in the letter that Mountbatten writes to Charles is what I really believe -- you know, based on everything I've read and people I've spoken to, that that represents his view.

"We will never know if it was put into a letter, and we will never know if Charles got that letter before or after Mountbatten's death but in this particular drama, this is how I decided to deal with it," he added.

Critics of the show have argued that the latest series includes a raft of falsehoods.

"People actually do believe it because it is well filmed, lavishly produced, well acted with good actors. You can't just dismiss it as tabloid rubbish," Hugo Vickers, historian and author of "The Crown Dissected," told CNN.

"In this particular series, every member of the royal family, in my view, comes out of it badly, except the Princess of Wales," he said. "It's totally one sided, it's totally against Prince Charles."

Vickers told CNN that the show contains a number of "mischievous" inaccuracies -- including scenes which show Queen Elizabeth at odds with Thatcher -- adding that viewers could watch the show and assume it to be true.

"Anyone watching, they may say, 'I saw it on The Crown, it must be true.' It's not true," he added.

Last year, the British royal family denied any involvement with the Netflix series, after Morgan claimed to meet regularly with "people who are very high-ranking and very active within the organisation."

Donal McCabe, the Queen's communications secretary, said in a letter to the UK's Times, which Buckingham Palace subsequently forwarded to CNN: "The Royal Household has never agreed to vet or approve content, has not asked to know what topics will be included, and would never express a view as to the programme's accuracy."