Theirs was, perhaps, the most intriguing, most unlikely relationship in the entire royal drama. Princess Diana was just the kind of long-limbed and pretty girl he would have been attracted to had he been 30 years younger.
Prince Philip was a decisive and worldly man whose frankness she admired, the only man in the House of Windsor, she felt, who actually listened to her.
She once wondered out loud to friends: ‘How many other wives would discuss their marital problems with their father-in-law instead of their husband?’
But that is exactly what she did in the summer of 1992 when the world’s focus on her unhappy marriage to the Prince of Wales was the central crisis of the Queen’s ‘annus horribilis’.
Philip was the one figure within the family who was on familiar terms with the real world outside palace walls. His reputation as the Queen’s husband was of a short-tempered and sometimes brusque man who spoke his mind too freely.
But Diana had come to know another Philip, hard, yes, but understanding too. By the time of her death in 1997 she realised just how much she admired him.
Theirs was, perhaps, the most intriguing, most unlikely relationship in the entire royal drama. Pictured: Princess Diana and Prince Philip at the Royal Ascot in 1986
And he, a man who had lived more than a bit and understood a lot, had come, reciprocally, to admire her and also to understand why he felt such a well of sympathy for her.
He hadn’t always been a fan. At times the very mention of her name had been enough to send him into an angry tirade.
If she’d had enough of the Royal Family, he raged, she could get out and stay out.
Although he regarded Diana as hard-working, he doubted if the princess had any real sense of commitment to the institution that had elevated her to public prominence.
How different things had been just a few years earlier when Philip was told by his son Charles that he had proposed to Lady Diana Spencer and that she had accepted. Philip could relax at last, having been urging his 32-year-old son to find a bride.
She was sweet and inexperienced, and Philip went out of his way to make her feel welcome and comfortable. He made her laugh. He was very fond of her.
And he, a man who had lived more than a bit and understood a lot, had come, reciprocally, to admire her and also to understand why he felt such a well of sympathy for her. Pictured: Prince Philip greets Princess Diana at a dinner at the Royal Society of Arts in London in 1986
But eventually he began to notice – as did the Queen – that at times she could be, by palace standards at least, unreasonable. This included her apparently obsessive preoccupation with Mrs Camilla Parker Bowles within a year of the marriage, and soon after the birth of Prince William in 1982.
At the time he and the Queen were unaware of their son’s infatuation for Mrs Parker Bowles, who they saw from time to time on the arm of her husband, the popular Royal Family friend, Guards officer Andrew Parker Bowles.
Throughout this early period Philip was increasingly baffled by what he saw as Diana’s irrational and unpredictable behaviour.
The sweet-natured girl who had charmed the Royal Family on her first visit to Balmoral was morphing into a tetchy, discontented princess. They assumed her problems were most likely caused by post-natal depression.
In fact they were at that time unaware that Diana was suffering from the eating disorder bulimia nervosa, which was to cast such a shadow over her life for the next decade or so.
Whatever the early cause of her unhappiness, Philip had considerable sympathy for her.
At the time he and the Queen were unaware of their son’s infatuation for Mrs Parker Bowles, who they saw from time to time on the arm of her husband, the popular Royal Family friend, Guards officer Andrew Parker Bowles. Pictured: Prince Charles speaking to Camila Parker Bowles at a Polo Match in 1975
She was, after all, an outsider like himself who had married into the Royal Family and was having to cope with the stresses and responsibilities of her new role in life. Pictured: Prince Philip pictured next to Charles and Diana on their wedding day
For Diana, the very fact that one of the royals – and a key one at that – was sympathetic towards her, and actually showed it, meant a great deal
She was, after all, an outsider like himself who had married into the Royal Family and was having to cope with the stresses and responsibilities of her new role in life.
For Diana, the very fact that one of the royals – and a key one at that – was sympathetic towards her, and actually showed it, meant a great deal. She believed no one else in her husband’s family, so absorbed in their own interests, really cared.
By now Philip and the Queen had been made aware that Prince Charles was sleeping with the wife of a brother officer, and they strongly disapproved.
All the same, Philip’s sympathy for Diana was not without its limitations. He strongly objected to an assertion that Diana made, implying he had quietly given Charles a green light to resume his old affair with Camilla once he and Diana had been married for five years.
He wondered whether the princess was exaggerating her unhappiness and using Mrs Parker Bowles as an excuse.
Privately, Philip confided to a friend that he and the Queen had always had ‘the highest hopes’ for Charles and Diana as a couple in love. Pictured: Princess Diana and Prince Philip at a Polo Match in 1987
He admitted he couldn’t believe that his son was cheating on such a beautiful young wife, this despite the tradition of extramarital privileges enjoyed by so many male members of the Royal Family down the generations.
At the same time, Prince Philip made it clear that he hoped that Diana was prepared to accept the drawbacks as well as the advantages that went with being married to a Windsor.
Privately, he confided to a friend that he and the Queen had always had ‘the highest hopes’ for Charles and Diana as a couple in love. Even so, nothing prepared him for the shock of her revelations in the Andrew Morton book in the summer of 1992.
He read it from cover to cover, having been briefed that Diana had helped the author, a claim which she vehemently denied at the time.
The disclosures, including her accusations that the family didn’t care about her unhappiness, left him anguished and furious. He thought her account must be ‘biased’. And yet the deep-seated sympathy that he felt for her being trapped in a marriage to a man who, it was now clear, was in love with another woman, did not waver.
His first instincts, however, were to rationalise his son’s behaviour, and when an exchange of frank letters with Diana began that summer, the rough-tongued ex-sailor pithily put some unflinching questions on the page.
What is clear is that while Charles and other family members were anxious to wash their hands of the troublesome princess, Philip was trying to find a way of keeping her within the family. Pictured: A pregnant Princess Diana stands next to Prince Philip at the Trooping of the Colour ceremony in 1982
‘Can you honestly look into your heart and say that Charles’s relationship with Camilla had nothing to do with your behaviour towards him in your marriage?’ he asked her in one letter. He also suggested to her that she had not been a caring wife and that, while she was a good mother, she had been too possessive with William and Harry.
Jealousy, he said, had eaten away at the marriage and her irrational behaviour had not helped.
He also reminded the princess that her husband had made a ‘considerable sacrifice’ cutting ties with Camilla during the early years of the marriage and that Diana had not ‘appreciated what he had done’.
In another letter he crisply informed her that being the wife of the heir to the throne ‘involved much more than simply being a hero with the British people’. Diana was devastated by some of the points he made.
And yet she felt an integrity in everything he was suggesting. What is clear is that while Charles and other family members were anxious to wash their hands of the troublesome princess, Philip was trying to find a way of keeping her within the family.
Jealousy, Philip said, had eaten away at the marriage and her irrational behaviour had not helped. Pictured: Prince Philip, Prince Charles and Princess Diana and Prince William, who is holding his hand over his eyes, stand on the balcony of Buckingham Palace for the Trooping the Colour ceremony in 1988
His attitude towards Diana was completely different from the attitude he showed to the Duchess of York after her toe-sucking extra-marital shenanigans were publicly exposed in a red-top newspaper, to the huge embarrassment of the Royal Family. When Fergie walked into a room – she occasionally has tea with the Queen – he would walk out.
All his letters to Diana he signed ‘With fondest love, Pa’, and he always referred to himself and the Queen as ‘Pa and Ma’. Diana continued to call the Queen ‘Ma-ma’, and Philip ‘Pa’ until her death.
What she happily took to be her father-in-law’s true colours emerged in another letter in which he wrote: ‘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.
‘I cannot imagine anyone in their right mind leaving you for Camilla. Such a prospect never even entered our heads.’
Diana was in her apartment in Kensington Palace when she opened and read this letter from her father-in-law. She skipped joyously about the room.
This was what Philip the man, rather than Philip the royal prince, really thought about his eldest son’s insistence on trading in the lissom Diana for an older woman.
It was what his friends thought as well. As one laconically observed, after hearing that Charles was digging in his heels and refusing to give up Camilla: ‘Not many men would fight a duel over her.’
All his letters to Diana he signed ‘With fondest love, Pa’, and he always referred to himself and the Queen as ‘Pa and Ma’. Pictured: Princess Diana and Prince Philip at a Polo Match in 1987
So here was Prince Philip trapped between his loyalty to his son and family and his incomprehension at Charles’s infatuation for Mrs Parker Bowles, and having to feel his way cautiously between the two.
Charles had, of course, always tried to live up to the womanising reputation that his handsome father enjoyed when young, producing a string of pretty conquests. But ultimately, here he was, drawn to the well-bosomed comforts of a slightly older woman of experience.
‘Prince Philip recognised that this was a crucial factor in Diana’s unhappiness,’ explained a senior courtier. ‘And she took great comfort in knowing he felt this way.’
Madame Lucia Flecha de Lima, the late wife of the former Brazilian ambassador to London, and who became a close friend of Diana, also recognised the special relationship that emerged between the princess and the duke.
‘I personally read around half a dozen of the letters from Prince Philip,’ she recalled. ‘Diana let me see them. And although they were tough, it was clear to me he was trying to be constructive.
‘They were warm and kind, courteous and helpful, like a father writing to a daughter.
‘He drew on his own experiences. In one letter he wrote about how, when he and the Queen married, they thought they would have some years together living their own lives, but it was not to be and “Ma” was called to her duty, and he had to give up the career he loved.’
So here was Prince Philip trapped between his loyalty to his son and family and his incomprehension at Charles’s infatuation for Mrs Parker Bowles, and having to feel his way cautiously between the two. Pictured: Charles and Diana in Maitland, New South Wales, Australia in 1983
Madame de Lima added: ‘Philip felt Diana and Charles did not have to be divorced. They could live separate lives, with separate apartments, if necessary, but they could remain together.’
For her part, Diana’s flow of letters to Prince Philip were filled with the pain and frustrations of a young married mother whose husband’s ardour was focused on another woman.
She showed his letters to several of her friends who helped her construct replies that were as unblinking as his had been.
This remarkable exchange of letters ended when the princess and Charles separated in December 1992. Diana continued to see both Ma and Pa at formal royal occasions, Philip always taking an interest in what she was doing.
Significantly, however, in the wake of her Panorama interview in which she claimed there were ‘three people’ in the marriage, it was the Queen who wrote to her, not Philip.
The prince was said to have gone ‘ballistic’ at her interview. And although he was no longer corresponding with her himself, he forcefully told the Queen she must use her authority.
She suggested that the couple would be better off divorced. Prince Philip agreed. By now his patience had run out.
He was angry with Diana, not so much because of her admission of an affair with James Hewitt – he knew about that – but because of her belittling comments about Charles in the Panorama interview, particularly that he was unsuited to be king.
Philip recognised, however, that her emotional TV outburst was a response to Charles’s own television admission of adultery with Camilla. In the years that followed, his views of Diana soured, especially over what he saw as the princess upstaging the Queen on the public stage.
All the same, Diana remained thankful for Philip’s intervention at the height of her misery over her marriage until the day she died.
For his part, even after Charles married Camilla, ushering in a welcome period of calm, the duke never entirely got over his disappointment that all his efforts had failed to save his son’s first marriage.