British actors have been told not to audition for the role of a young Duke of Cambridge in a forthcoming film about Diana, Princess of Wales, due to new rules faced by the country post-Brexit.

A casting invitation posted online calls for boys aged between nine and 12 to apply for the role of the prince, when he was aged 11, in the upcoming biopic, Spencer.

However, it says only European passport holders can apply and “NOT British-European due to new Brexit rules from 1st January 2021.”

Amy Hubbard, the casting director on the film, later said in a post on Twitter that it was common practice for key roles in films to be filled with actors who share their citizenship with the project’s financiers.

She said: “It’s not about travel. It’s common on films that the passport for significant characters needs to match that of the financiers.”

The film, which stars Kristen Stewart as Diana and is directed by Pablo Larrain, follows the princess as she spends a weekend in Sandringham during which she realises her marriage to the Prince of Wales is failing.

Charlie’s Angels UK Premiere – London
Kristen Stewart (Ian West/PA)

It is reportedly due to start shooting in Germany early next year.

A number of actresses have played Diana in the past, including in 2013 when Naomi Watts took up the role in a biopic titled Diana.

Oliver Hirschbiegel’s film was panned by critics.

In 2007, Genevieve O’Reilly played the royal in Channel 5 film Diana: Last Days Of A Princess.

Last year, Emma Corrin was cast as Diana in Netflix series The Crown and she made her debut this month.