Prince Philip and Princess Diana may not seem like two figures who had much in common at first. But both the Duke of Edinburgh and the Princess of Wales had to weather life in the royal family as outsiders.
It's one thing to be born into the Firm, but life as someone marrying in can be immensely challenging. At first, those challenges bonded Philip and Diana. Philip took Diana under his wing in a lot of different ways. As her marriage to Prince Charles struggled, he took to writing her letters, hoping to ease her mind and offer her some perspective.
As things got worse between Diana and Charles, Philip's attempts to help felt more like additional judgment and pressure. Diana began to resent his suggestions, while Philip began resenting how hard she was making things for the monarchy. Still, there was some feeling of their former relationship that always lingered.
When Princess Diana married into the royal family in 1981, she learned what it means to marry your partner's family. Diana made the best of her life in an unusual and extraordinary family by finding allies where she could. Among them was Prince Philip.
Like Philip had at first, Diana found the restrictions of life as a member of the royal family hard to deal with. Philip took the opportunity to take Diana under his wing and try to teach her how to make the best of the unusual lifestyle.
"When (Diana) found the restrictions of royal life difficult, it was Philip who helped her," writes royal author Ingrid Seward. Her new book, Prince Philip Revealed, has been previewed by People.
"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," Ingrid continued.
"Diana found the Balmoral dinners a massive strain and the atmosphere stifling. 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."
Somehow, Diana and Philip managed to have some sort of bond, even as her marriage to Charles began going south. The publication of Andrew Morton's tell-all 1992 book Diana: Her True Story began posing more difficulties. After its publication, the Queen and Philip called Charles and Diana to a family meeting at a private sitting room at Windsor Castle.
Philip asked the couple to "try to think of their children, the monarchy and the country instead of their personal woes," Ingrid writes in the book.
Philip also made an effort to be gentler with Diana and began writing her letters, affectionately signed "Pa."
In 2003, former royal butler Paul Burrell leaked the letters in his book, A Royal Duty. In particular, Philip wrote in one that he disapproved of his son's affair with Camilla Parker Bowles.
"I cannot imagine anyone in their right mind leaving you for Camilla," he allegedly 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. Such a prospect never even entered our heads."
In another letter, Philip allegedly wrote, "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."
Diana replied to Philip, "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."
There were also reportedly less-affectionate letters in which the two tensely debated, which were addressed by Philip in a statement in 2003.
"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," the statement read.
"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."
Resentment grew between Philip and Diana as her marriage to Charles came to an end. There was a feeling that he was too involved as an in-law on Diana's part, while he resented the difficulties she was presenting to the Firm.
The two were not on great terms at the time of Diana's death in 1997. Philip stepped up for his grandsons at that time, knowing the pain of losing loved ones at a young age. He walked with them behind Diana's casket at her funeral.
