Princess Diana and Sarah, Duchess of York, were once close friends, sharing regular lunch dates and were dubbed the Merry Wives of Windsor by the press.

Even before entering the royal fold, they ran in the same social circles and met as children as their mothers went to school together.

Diana’s former butler Paul Burrell wrote in his latest book, Royal Insider that ‘Fergie formed a friendship with Diana, Princess of Wales, from the beginning of 1982′.

He said: ‘They would discuss the dour men in grey suits within the Royal Household, nicknamed “the enemy within”.

‘Diana, having been in the Royal Family for five years, was able to offer Sarah some sage advice on the dos and don’ts, whom she could trust and a rather lengthy list of those with whom she should be cautious.

‘It was tragic that the relationship between them disintegrated after the publication of Sarah’s autobiography, My Story, in 1996.

‘Although Diana supported Sarah’s decision to go public and become an independent woman, her support came with conditions.

‘Diana requested that Sarah not talk about her, her boys or their relationship, but it was too much to ask.

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Princess Diana and Sarah, Duchess of York, were once close friends, sharing regular lunch dates and were dubbed the Merry Wives of Windsor by the press

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The relationship broke down after the publication of Sarah’s autobiography, My Story, in 1996

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Diana’s former butler Paul Burrell wrote in his latest book, Royal Insider: ‘Fergie formed a friendship with Diana, Princess of Wales, from the beginning of 1982’

‘When the book was published, Diana was furious that throughout its pages, there were references to her, William and Harry.

‘Many thought that the fallout was caused by Sarah suggesting that she had contracted verrucas from shoes given to her by Diana, but that was not the case. Diana felt used and refused to speak to Sarah.’

Like Prince Philip’s famous letters to Diana, the women resorted to writing to one another.

Burrell wrote that the final blow came when a letter arrived purportedly from Princess Eugenie, Sarah’s daughter, with the envelope written in a child’s hand and addressed to HRH The Princess of Wales.

He wrote: ‘Diana said to me, “Look at this”, as she held the letter head high.

‘”She is now using her children to intervene. It’s her last resort?”

‘Diana was incandescent with rage. The relationship was terminated for good, and they never spoke again.

‘Diana’s last words to Sarah were that when it came to honesty, perhaps she shouldn’t resort to using her child to address envelopes to Diana and that Diana was happier than she had ever been.’

There was also the matter of Diana meeting the son of President John F Kennedy.

Andrew Lownie wrote in his book, Entitled: The Rise and Fall of the House of York, that Sarah’s ‘schoolgirl crush’ almost came between the pair.

According to Lownie, Sarah invited Kennedy Jr out for drinks back in 1996. At the time, she was recently divorced from Prince Andrew.

Lownie claimed that the Duchess was aware that Kennedy Jr was then dating actress Daryl Hannah.

‘That’s not going to bother me!’ she reportedly said.

‘But it bothered Hannah, and Kennedy cancelled, claiming a prior engagement,’ Lownie wrote.

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Andrew Lownie wrote in his book, Entitled: The Rise and Fall of the House of York, that Sarah’s ‘schoolgirl crush’ almost came between the pair

‘Staff were then ordered to spy on his apartment all night to check that he had told the truth.

‘She was not to be discouraged, especially after learning that Princess Diana had met Kennedy for 30 minutes at Christmas 1995 at a New York hotel.

‘She was furious: “He’s mine! Why can’t she just leave him alone?”‘

The author also claimed that Sarah’s code name for Kennedy Jr was ‘Number Nine,’ signifying ‘his place in the order of her lovers’.

She reportedly spent hours reading about him in magazines and would even cut out photos of him wearing swimsuits.

A 2024 biography co-written by Kennedy Jr’s former assistant and longtime confidant, RoseMarie Terenzio, revealed that Diana met him ‘partly’ to make Sarah jealous.

‘It was never made public, so that made it quite fun, actually,’ Diana’s private secretary and equerry, Patrick Jephson, wrote in JFK Jr: An Intimate Oral Biography.

‘Diana wanted it to be discreet because it had all the makings of a great gossip story, didn’t it? The world’s most eligible bachelor wasn’t he at the time?

‘And she had just gotten unmarried or was in the process of getting unmarried. It would’ve been a rather intriguing thing to dream about.

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Sarah is pictured leaving Westminster Abbey with her two daughters Eugenie and Beatrice after the funeral service for Diana on September 6, 1997

‘She didn’t want that, but she was curious to meet him. Partly, I think, because Sarah Ferguson had the hots for him and Diana wanted to, I think, do one up on her.’

When Diana died on August 31, 1997, she had not spoken to her former best friend and sister-in-law in months.

According to Burrell, Diana’s death was particularly difficult for the Duchess of York, whom he described as being ‘all at sea’ when she heard the news.

Burrell said: ‘She didn’t have anyone to lean on or rely on like Diana, and she missed her very much. I think she still misses her to this day because they were such great friends.’

In her 2011 memoir Finding Sarah: A Duchess’s Journey to Find Herself, she wrote of her friendship with Diana.

She said: ‘Diana was one of the quickest wits I knew; nobody made me laugh like she did.’

‘We took vacations together with our children. Sadly, at the end of Diana’s life, we hadn’t spoken for a year, although I never knew the reason, except that once Diana got something in her head, it stuck there for a while.’