'The Crown' risks infuriating the royal family by exploring the relationship between Prince Philip and aristocrat Penny Bradbourne.
Natascha McElhone has joined the cast of the hit Netflix series as Brabourne, with the upcoming series delving into the close relationship she had with the late Duke of Edinburgh – who will be portrayed by Sir Jonathan Pryce – in the 1990s, when the fifth season takes place.
The relationship led to "raised eyebrows" at the time as there was a 32-year-age gap between Philip, who died aged 99 in April, and Penny.
An insider told The Sun newspaper: "This is a relationship which naturally raised a few eyebrows and sparked quite a few whispers, but Philip and Penny maintained they were just good friends.
"The makers of 'The Crown' believe it is a relationship worthy of exploring and casting a veteran actor like Natascha is a reflection of how high profile the role is.
"But the highly personal relationship is unlikely to be welcomed as a storyline by Her Majesty or the rest of the royal family."
The series previously sparked controversy in the second series by portraying Philip as a flirtatious man with an eye for the ladies.
'The Crown' has undergone a cast refresh for the new season with Imelda Staunton taking over from Olivia Colman as Queen Elizabeth. Dominic West, Elizabeth Debicki and Lesley Manville have joined the show as Prince Charles, Princess Diana and Princess Margaret. Johnny Lee Miller will also feature as John Major, the Prime Minister at the time.
The series will cover the royal events of the 1990s, including Diana's death in a 1997 car crash in Paris.
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