The letters Prince Philip and Princess Diana exchanged before her divorce from Prince Charles

In the leadup to her divorce from Prince Charles, Princess Diana received some relationship advice from an unlikely source: her father-in-law.

The Duke of Edinburgh and Diana exchanged several hand-written letters throughout 1992, following the Prince and Princess of Wales' high-profile separation.

Many of the notes were read aloud during the inquest into Diana's death, and have now been resurfaced in an episode of The Royal House of Windsor on Channel 4 in the UK.

In one message, the Queen’s husband candidly expressed his disapproval of his son’s affair with Camilla Parker Bowles, who was married at the time.

“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 in another note.

LISTEN: The Life Bites podcast explores the tricky terrain of divorce and what it means to end a marriage. (Post continues.)

However, the Duke of Edinburgh also offered his support and guidance to the couple as they navigated their separation.

“I can only repeat what I’ve said before, if invited, I will always do my utmost to help you and Charles to the best of my ability,” he wrote to Diana.

“But I am quite ready to concede that I have no talent as a marriage counsellor!!!”

In her response letters, addressed “Dearest Pa” and signed off “With my fondest love”, Diana seemed touched by her father-in-law’s thoughtfulness.

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"This last letter of yours showed great understanding and tact, and I hope to be able to draw on your advice in the months ahead, whatever they may bring.”

Diana also acknowledged the ramifications of her very public separation from Charles on the rest of the Royal Family.