The society wedding of the year is less than three weeks away, yet King Charles and Queen Camilla have still not confirmed their attendance, I hear.

And the delay has provoked fevered speculation among friends and family of the Duke of Westminster, Hugh Grosvenor, and his bride-to-be, Olivia Henson.

'Their Majesties have not forgotten what happened at the wedding of Hugh's sister,' a source tells me. 'There is still a lot of tension that exists.'

The King and Queen chose to turn down their invitations to the 2004 wedding of the duke's sister, Lady Tamara Grosvenor, and Edward van Cutsem, a godson of His Majesty. It was held at the same venue as the duke's wedding next month: Chester Cathedral.

Camilla Parker Bowles, as she was then, had been told that she would not be allowed to sit with Prince Charles and would instead be seated several rows back and be made to arrive separately. This was because Queen Elizabeth and Prince Philip attended the ceremony, along with Princes William and Harry.

The society wedding of the year is less than three weeks away, yet King Charles and Queen Camilla have still not confirmed their attendance, I hear.

Duke of Westminster, Hugh Grosvenor, and his bride-to-be, Olivia Henson. The King and Queen's delay has provoked fevered speculation among friends and family. 'Their Majesties have not forgotten what happened at the wedding of Hugh's sister,' a source tells me. 'There is still a lot of tension that exists.'

Harry and Meghan have already been excluded from next month's wedding, even though Hugh, who has an estimated fortune of £10billion, is reportedly the godfather of their son, Prince Archie. Hugh is believed to have felt the Sussexes' appearance could cause tensions with the Royal Family

According to royal author Sarah Bradford, Camilla was so infuriated that she told Charles the status quo was no longer acceptable. Their own engagement was announced three months later

'Her Majesty is a stickler for protocol,' a courtier explained at the time. 'It would be inappropriate for Mrs Parker Bowles to sit beside Prince Charles since she has no official standing.'

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Tensions were heightened by reports that Emilie van Cutsem, the groom's mother, and Camilla had fallen out after each is alleged to have criticised the behaviour of the other's children.

Charles ultimately excused himself from the event with just days to go, saying he had to visit Warminster barracks to meet the families of soldiers serving in Iraq. Camilla was described as 'otherwise engaged'.

According to royal author Sarah Bradford, Camilla was so infuriated that she told Charles the status quo was no longer acceptable. Their own engagement was announced three months later.

The Duke and Duchess of Sussex have already been excluded from next month's wedding, even though Hugh, who has an estimated fortune of £10billion, is reportedly the godfather of their son, Prince Archie.

Hugh is believed to have felt the Sussexes' appearance could cause tensions with the Royal Family. Harry is said to have been sent a 'save-the-date' email in error.

The wedding of Lady Tamara Grosvenor, and Edward van Cutsem.  The King and Queen chose to turn down their invitations to the 2004 wedding

Chester Cathedral where the duke's wedding is set to take place next month

Hugh is believed to have felt the Sussexes' appearance could cause tensions with the Royal Family. Harry is said to have been sent a 'save-the-date' email in error

Prince Harry and Prince William at the wedding of Edward van Cutsem and Lady Tamara Grosvenor in 2004 

The Prince and Princess of Wales and their elder son, Prince George, who is Hugh's godson, are invited to the wedding. However, Catherine is not expected to attend because she is undergoing cancer treatment

However, sources 'close to' the Sussexes later said: 'Harry called Hugh and said it would be too awkward if he and Meghan Markle attended, so he made his apologies and Hugh understood.'

The Prince and Princess of Wales and their elder son, Prince George, who is Hugh's godson, are invited to the wedding. However, Catherine is not expected to attend because she is undergoing cancer treatment.

A Buckingham Palace spokesman declines to comment. The Duke of Westminster's spokesman is similarly silent.