Inside Prince Philip's Rocky Relationship with Princess Diana — and Their Personal Letters
The royal "outsiders" were initially close but gradually drifted apart as Diana's relationship with Prince Charles collapsed
Having married into the royal family in 1947, Philip — who died on Friday at age 99 — could understand the difficulties of being an "outsider" in the world's most famous family. He was also "initially charmed" by the beautiful, fun-loving princess as she struggled to adapt to her new position in life.
"When (Diana) found the restrictions of royal life difficult, it was Philip who helped her," writes royal author Ingrid Seward in her new book Prince Philip Revealed, excerpted in the first issue of PEOPLE Royals. "Once she was married, she never sat next to her husband; she was always sat next to Philip at the endless black-tie dinners, and he took care of her.
"Diana found the Balmoral dinners a massive strain and the atmosphere stifling," Seward continues. "When the piper came around the table after dinner with his kilt swirling and his pipes whining, she couldn't wait to leave the room."
This bond continued after the publication of Andrew Morton's tell-all 1992 book Diana: Her True Story, which revealed the full extent of Diana's struggles during the collapse of her marriage to Prince Charles.
In the aftermath of the book's publication, the Queen and Philip arranged a family meeting with Charles and Diana in their private sitting room at Windsor Castle – a moment captured in season 4 of the hit Netflix drama, The Crown.
During the conversation, Philip asked Charles and Diana to "try to think of their children, the monarchy and the country instead of their personal woes," says Seward.
Away from view, the Duke of Edinburgh also privately adopted a much gentler approach and started writing letters to Diana, in the hope that he could subtly influence her.
"He tried to make her face facts and deal with the problems within her marriage, explaining he knew first-hand the difficulties of marrying into the royal family," says Seward.
Philip signed the letters "Pa," and initially sympathized with Diana's plight, even going so far as to say that Charles "was silly to risk everything with Camilla."
"We never dreamed that he might feel like leaving you for her. I cannot imagine anyone in their right mind leaving you for Camilla," he added in one of the notes. "Such a prospect never entered our heads."
In another letter, Philip offered to do everything in his power to save their marriage.
"If invited, I will always do my utmost to help you and Charles to the best of my ability. But I am quite ready to concede that I have no talent as a marriage counselor," he wrote.
Sadly, the letters failed to heal the enormous rift in Diana's marriage. Over time the bond between the two royal outsiders also crumbled as steadily as Diana's relationship with Prince Charles — partly because Philip told the princess she was wrong to have her own extra-marital affairs.
"(Philip) realized that Diana's behavior was having a detrimental effect on the institute of the monarchy," Seward adds in Prince Philip Revealed.
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Diana, meanwhile, "came to dislike Prince Philp as she found him impossible to deal with," Seward continues. "He might be entertaining as a dinner guest" (Diana) explained, "but as a father-in-law he was too judgmental."
Despite this, Diana did at least appreciate the motive behind Philip's letters as her marriage floundered in 1992. Eleven of the "outsiders" notes were revealed during the 2007/2008 inquest into the tragic deaths of Diana and Dodi Fayed in August 1997.
"Dearest Pa, I was particularly touched by your most recent letter, which proved to me, if I did not already know it, that you really do care," Diana wrote in reply to Philip's "marriage counselor" letter. "You are very modest about your marriage guidance skills, and I disagree with you!"
Another said, "I was so pleased to receive your letter, and particularly so to read that you are desperately anxious to help."
Diana also said that she appreciated her father-in-law's "great understanding and tact" — not qualities Philip was exactly famous for during his near-century long life. Tellingly, the princess signed off all of her letters to the Duke with endearments such as "with my fondest love."
Yet even the secret correspondence could not survive the devastation of Diana's collapsed marriage. The inquest heard that by 1994 and 1995, Philip's letters to Diana were of a very different tone.
Her friend, alternative therapist Simone Simmons, told the 2007/2008 inquiry that Diana showed her "two letters that really upset her." Lawyer Michael Mansfield then asked Simmons if the letters were "extremely derogatory" about Diana? "Yes and very cruel as well," Simmons replied, adding that they left Diana "red in the face."