As Lady Sarah McCorquodale celebrates 44 years of marriage today, onlookers may wonder if she is reflecting on how different her life could have been.

Because Princess Diana‘s eldest sister once dated Prince Charles – she went out with the heir to the throne two years before her sister.

In fact, Lady Sarah, 69, even introduced Diana to Charles and says she played ‘cupid’ for the pair.

But it was 22-year-old Lady Sarah Spencer, a willowy red-head with a great sense of fun, who first caught Prince Charles’s eye at a house party at Windsor Castle for Royal Ascot.

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Prince Charles talks to Lady Sarah Spencer at a polo match in Windsor, 1977

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Prince of Wales at polo with Princess Diana’s sister, Lady Sarah, whom he dated in 1977

‘Prince Charles enjoyed Sarah’s sparkiness and irreverent wit and they made each other laugh,’ says Sarah Bradford, author of Diana: Finally, the Complete Story.

Their romance involved polo matches and an invitation to Balmoral but it was after a skiing trip to Klosters in 1978, that Sarah made the mistake that would end their liaison.

In an astonishingly frank interview with Woman’s Own, Bradford’s biography reports that Sarah declared: ‘I’m not in love with Prince Charles.

‘I’m a whirlwind sort of lady, as opposed to a person who goes in for slow-developing courtships.

‘I can assure you that if there was to be any engagement between Prince Charles and myself, then it would have happened by now.’

Time magazine also reported that Sarah said, ‘Charles makes me laugh a lot. I really enjoy being with him,’ but she said there was ‘no chance’ of her marrying him.

‘I’m not in love with him. And I wouldn’t marry anyone I didn’t love whether he were the dustman or the King of England.’

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Princess Diana at Charles Spencer’s 21st with Prince Charles and sisters, Lady Sarah (far right) and Lady Jane Fellowes

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Sarah is known for her love of cigarettes, seen here at the Kensington roof Gardens in 1979

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Earl Spencer and his first wife with Queen Elizabeth the Queen Mother at Westminster Abbey after the christening of their daughter Sarah, 1955

Sarah also described Charles as a ‘romantic who falls in love easily’ and revealed that despite their closeness, she always called him ‘sir’.

Naturally upset by her revelations, Charles allegedly told Sarah that she had done something ‘stupid’ and their relationship met its end.

Yet there were no hard feelings and Sarah later prided herself on being the matchmaker for Diana and Charles.

The pair met at a dance at Althorp – the Spencer family estate – when Diana was just 16.

‘I introduced them, I’m cupid,’ Sarah is reported to have said.

It seems that for Sarah, a more humble marriage to a wealthy Lincolnshire farmer – rather than toiling on the royal frontline – was the true path to happiness.

Her husband Neil McCorquodale, now 73, is reported to be ‘solid, very steady, private, quiet, with a good sense of humour’, according to Sally Bedell Smith, author of Diana in Search of Herself: Portrait of a Troubled Princess.

The former officer with the Coldstream Guards was the perfect foil for Sarah, who Bedell Smith says, ‘was ebullient and enterprising, with an unpredictable streak.’

So on May 17, 1980, the couple married in a modest ceremony at St Mary’s Church near Althorp, the Spencers’ ancestral seat in Northamptonshire.

Lady Sarah, who wore a lace gown with a high neck and peplum detail, held a modest bouquet of seasonal white flowers, and topped off her look with the Spencer family diamond tiara.

Princess Margaret’s daughter Lady Sarah Armstrong-Jones (now Lady Sarah Chatto) was a bridesmaid.

After marriage, Lady Sarah and Diana remained close – the sisters would go on holiday with their children, and Sarah even became one of Diana’s ladies-in-waiting between 1992 and 1997.

It was a reversal of their childhood dynamic in which Diana hero-worshipped her big sister, even being a cleaner at a rental house that Sarah managed for their father.

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Lady Sarah with Neil McCorquodale, who she married in May 1980

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Lady Sarah Spencer married Neil McCorquodale at St Mary’s Church, near Althorp, on May 17, 1980. Lady Sarah Armstrong Jones (back row) was a bridesmaid

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The Christening of Emily Jane McCorquodale, in Lady Sarah’s arms, in Lincolnshire

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Both sisters remained close after marriage and often holidayed together. Above: Lady Sarah (right) with her famous sister at Wimbledon, 1981

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Princess Diana laughing with her two sisters, Lady Sarah and Lady Jane Fellowes, 1995

Sarah’s support may even have extended to turning a blind eye to the ups and downs of Diana’s love life. In 1998 Princess Diana biographer Judy Wade told People magazine, ‘I think Sarah knew about Diana’s affairs.

‘In a way, she even encouraged Diana to be wild and to have lovers.’

In fact, Diana once called Sarah, ‘the only person I know I can trust’.

The closeness between the sisters was evident even after Diana’s death, when Lady Sarah read a poem at Diana’s funeral, acted as co-executor of Diana’s will and became president of the Diana, Princess of Wales Memorial Fund until it closed in 2012.

Today Sarah and Neil live near Grantham, Lincolnshire, where, in 2009, she served a one-year term as High Sheriff of Lincolnshire.

And it seems that Sarah is in no hurry to relinquish her reputation for being a bit wild – her friends and family celebrated her 60th with a huge cake in the shape of a packet of Silk Cut in tribute to her love of cigarettes.

Their three adult children, Emily, 40, George, 39, and Celia, 35, are close to their Windsor cousins.

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Sarah’s daughter Emily married George Woodhouse in Lincolnshire with Prince Harry and Meghan Markle amongst the wedding guests. Above: The special day in 2018

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Neil McCorquodale and Lady Sarah McCorquodale attend the wedding of Prince Harry and Meghan Markle, May 2018

Will and Harry kiss their aunts at unveiling of Diana statue

And Sarah and her other sister Lady Jane Fellowes are regular features of William and Harry’s lives: Sarah was at both of their weddings, as well as the christening of Harry’s son Archie in 2019.

In fact, Harry is thought to particularly identify with his Spencer family.

Ingrid Seward, royal commentator and editor of Majesty magazine, says that Harry is ‘extremely proud of his Spencer heritage’.

‘Not only does Harry look very Spencer with his red hair, but he calls his aunts Sarah and Jane his “red aunts”.’

She told the Telegraph’The Spencer family [is] known for being outspoken, all action, leading with the heart, not the head.’