Prince Philip has died at the age of 99, Buckingham Palace confirmed on Friday.
The Duke of Edinburgh died “peacefully” at Windsor Castle on the morning of 9 April, according to a palace statement.
Philip was the father of Prince Charles, whose marriage to Diana was the subject of tabloid scandal in the 1980s and 1990s.
The Duke of Edinburgh’s relationship with the mother of his grandchildren has been the subject of much speculation over the years, with conflicting reports of whether the pair had any affection for each other.
Here, we examine what is known about the late duke’s relationship with his daughter in law.
Both were ‘outsiders’ to the <strong>royal family</strong>
Prince Philip and Princess Diana were vastly different in age and came from different backgrounds (the Duke of Edinburgh was the son of Prince Andrew of Greece and Denmark, while Diana, though an aristocrat, was technically a commoner).
However, what they did have in common was the fact that they both married into the royal family, making them both outsiders.
Tobias Menzies, who plays Prince Philip in Netflix’s royal drama The Crown remarked on this commonality in an interview with People magazine last year.
"I guess there are some similarities in that, you know, it’s another outsider, a position that he obviously has been in. Maybe he has some kind of appreciation for the challenges that she’s going through," he said.
"I think on a very basic level, he just thinks it’s a good fit. In a slightly old-fashioned way, I think he also just liked her femininity, her beauty. He was sort of very seduced by her as well."
The pair exchanged affectionate letters
After Diana’s death, it was reported that she and Philip had exchanged letters, discussing her marital issues with his son, Prince Charles.
In 2003, former royal butler Paul Burrell leaked the letters, allowing the Mirror to print them as part of a serialisation of his book A Royal Duty.
Diana’s father in law reportedly wrote to her in summer 1992, telling her he disapproved of his son’s affair with Camilla Parker Bowles.
Philip’s alleged letter read: "I cannot imagine anyone in their right mind leaving you for Camilla."
It continued: "We do not approve of either of you having lovers.
"Charles was silly to risk everything with Camilla for a man in his position. We never dreamed he might feel like leaving you for her. Such a prospect never even entered our heads."
The Duke of Edinburgh signed off with "fondest love, Pa".
Diana appeared to also have a great deal of affection for Charles’s father. Some of their correspondence (which was heavily redacted) was revealed at the inquest of Diana and her partner Dodi Al Fayad in 2007.
The Princess of Wales called her father in law “Dearest Pa” and, when he said he would do his “utmost” to help her and Charles during their marital woes, she responded: “You really do care.”
In another letter presented at the inquest by the Duke of Edinburgh’s private secretary Brigadier Sir Miles Hunt-Davis, Diana wrote: “I would like you to know how much I admire you for the marvellous way in which you have tried to come to terms with this intensely difficult family problem.”
At times, their letter-writing reportedly became tense
Diana’s healer Simone Simmons also spoke at the inquest and said that Diana had later exchanged letters with her father in law in 1994 or 1995 which were far less affectionate.
“Diana read one out to me,” she said. “She was absolutely furious.”
However, in 2003, the Duke of Edinburgh gave an official statement refuting media reports that he wrote “insulting” letters to Diana.
The statement read: “The original letters sent by Prince Philip to the Princess have apparently been lost, but he kept copies of his letters to her and he also has the original replies from the Princess.
“He started the correspondence in June 1992 in a friendly attempt to resolve a number of family issues which arose at the time leading up to the official separation of the Prince and Princess of Wales in December of that year.
“Prince Philip wishes to make it clear that at no point did he ever use the insulting terms described in the media reports, nor that he was curt or unfeeling in what he wrote.”
The duke took his grandsons under his wing after Diana’s death
Following the Princess of Wales’s tragic death in a car crash in 1997, Prince Philip reportedly stepped up to support his grandsons, Prince Harry and Prince William.
Former Vanity Fair editor Tina Brown wrote about the Duke of Edinburgh’s behaviour after Diana’s passing in her 2007 book The Diana Chronicles.
"A member of the Balmoral staff noted that Prince Philip, who effectively lost his own mother at the age of ten when she was committed for three years to an asylum in Switzerland, was brilliantly effective with his grandsons, offering them gruff tenderness and outdoor activities like stalking and hiking to tire them out," she wrote.
When discussions took place about Diana’s funeral and how her sons, who were 15 and 12 at the time, should be involved, Brown said Philip spoke up for the boys.
"Stop telling us what to do with the boys," she claims Philip said.
"They’ve lost their mother! You’re talking about them as if they are commodities. Have you any idea what they are going through?"
Brown also said that Philip comforted his grandson William after he said he didn’t want to walk in his mother’s funeral procession, which Phllip called “a bloody parade”.
"If I walk, will you walk with me?" Philip reportedly said.
Philip later did walk alongside the boys as they walked behind their mother’s coffin.
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies