Spencer writer says the Diana biopic's most shocking details are true

One of the screenwriters behind Spencer the new Princess Diana biopic starring Kristen Stewart has spoken out about the reality behind some of the film's most shocking details, saying that, "All the things in the film that seem least believable are true."

During a recent interview screenwriter Stephen Knight (creator of Peaky Blinders and Taboo), explained that his research into the film wasn't solely based on books and documentaries and that instead he spoke to people who were actually present at Sandringham over the weekend in question.

The film focuses on one weekend in Diana's life. As she spends her Christmas holiday with the rest of the royal family at Sandringham and comes to the decision that she must end her marriage to Prince Charles.

"I know some people who knew Diana quite well," Knight told The Telegraph. "Let’s say… posh people. And they put me in touch with some other people who worked in the house on the occasion that the film is set," he explained, adding, "All the things in the film that seem least believable are true."

An example given by Knight is the weighing ritual: a Sandringham tradition in which everyone must be weighed on a set of antique scales at the beginning and end of their visit, to see how much weight they've put on during their stay.

The ritual was something which Knight had felt was particularly egregious given Diana's struggle with bulimia, sharing that "Christmas at Sandringham is basically a never-ending, inescapable series of meals."

Spencer is out in cinemas from November 5.