The new film will be a follow-up to the 2017 hit film Diana: In Her Own Words and is said to feature unheard recordings of the Princess of Wales for biographer Andrew Morton when writing his 1992 book, Diana: Her True Story.
He added: “We’re talking quite a bit about doing something for next year, which is the 25th anniversary of Diana’s passing and also coincidentally it’s the 30th anniversary of Andrew Morton’s book.
“There will be renewed interest, and season five of The Crown will be coming out.”
The previous documentary in 2017 garnered controversy as viewers heard Diana speak candidly about her personal life, mental health struggles, and marital discord with her then-husband Charles, Prince of Wales.
The paper reports that the new documentary could cause a similar upset at the Palace.
The Princess of Wales died in a car crash in Paris in 1997, with Charles going on to marry his long-term lover Camilla Parker Bowles in 2005.
The end of Charles and Diana’s marriage is due to be portrayed in the fifth season of Netflix’s royal drama The Crown next year, with Australian actress Elizabeth Debicki taking on the role of Diana from actress Emma Corrin.
The Affair star Dominic West is reportedly taking over from Josh O’Connor in the role of the Prince of Wales, while Olivia Williams is reported to be replacing Promising Young Woman writer-director, Emerald Fennell, in the part of Camilla Parker Bowles.
Elsewhere, Imelda Staunton will take on the role of The Queen, with Jonathan Pryce portraying Prince Philip, Duke of Edinburgh, and Lesley Manville performing as the Queen’s sister Princess Margaret, Countess of Snowdon.
*Diana: In Her Own Words and The Crown seasons 1 to 4 are available now on Netflix.