The Duke of Edinburgh tried his "utmost" to help the late Princess Diana during her marriage breakdown.

Prince Philip

Prince Philip

Prince Philip - who is the father of Charles, Prince of Wales - reportedly tried to help Diana and Charles' relationship by talking to both parties in the hope the pair would reconcile.

Royal expert, Ingrid Seward, wrote in his column on the Daily Mail: "First, Prince Philip tried to talk to Charles about his marital difficulties and the effect they were having on the royal institution. It was meant as fatherly advice, but because of the distant nature of their relationship, the conversations usually ended with Charles looking at his watch and making an excuse to leave the room.

"He also tried reaching out to his unhappy daughter-in-law by writing her dozens of letters.

"In one of these, he told her that he wished 'to 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 counsellor!'

"To start with, the letters -- which he signed 'Pa' -- were very sympathetic. He said that he knew first-hand the difficulties of marrying into the Royal Family and seemed to place much of the blame for her marital problems on Charles."

In the letters penned to the Princess of Wales - who split with Charles in 1996, one year before she tragically passed away - Philip acknowledged the pair had "lovers", but the 96-year-old royal admitted Charles's romance with Camilla, Duchess of Cornwall, was "silly" and a "risk".

Ingrid continued: "[Philip said] '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.'"

But Philip's "efforts" were unsuccessful, and he soon gave up on helping the duo and started to "snub" Diana.

Ingrid said: "But his efforts were to no avail. In June 1992, while the Queen and Philip were at Windsor Castle, the Sunday Times began to serialise Andrew Morton's book 'Diana: Her True Story.' They were stunned by what they read.

"As the second instalment of Morton's revelations was rolling off the presses, Diana attended Royal Ascot with the rest of the family. Quite deliberately, Philip snubbed her in full view of all the top-hatted people in the Royal Enclosure.

"Finally, a summit meeting was held at Windsor for the Prince and Princess of Wales to discuss the state of their marriage with Elizabeth and Philip.

"Diana maintained that the only solution was a separation, but the Queen hoped a compromise would be possible for the sake of the children and the monarchy. When the Princess failed to show up at a planned second meeting, Philip decided to take matters into his own hands. In further letters to Diana -- and occasionally face to face -- he let her know exactly what he thought in language that was blunt and to the point, though not meant to be unkind."

But Diana - who has sons Prince William, 35, and Prince Harry, 33 - did not take too kindly to the comments, which caused her relationship with Philip to "degenerate rapidly".

Ingrid explained: "Diana responded to that rap across her knuckles by announcing her retirement from public life, thereby turning rebuke to advantage and securing another sheaf of headlines of the kind that Philip had been so anxious to avoid.

"Her relationship with her father-in-law degenerated rapidly. She told her friend Teddy Forstmann, an American billionaire, that she hated the Duke -- and she said the same to me when I saw her at Kensington Palace shortly before her death."

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