The Princess of Wales has written a letter to the Irish Guards to apologise for not being able to take the salute and wish them luck for The Colonel’s Review in London on Saturday.

Kate, who is colonel of the regiment, spoke of her pride in them and added that being colonel “remains an honour”.

The letter said: “I wanted to write to you to let you know how proud I am of the entire regiment ahead of the Colonel’s Review and Trooping the Colour.

“I appreciate everyone trooping the colour this year has been practising for months, and dedicating many hours to ensuring their uniforms and drill are immaculate.

“Being your colonel remains an honour, and I am very sorry that I’m unable to take the salute at this year’s Colonel’s Review.

“Please pass on my apologies to the whole regiment, I do hope that I am able to represent you all once again very soon.

“Please send my very best wishes and good luck to all involved.

“Quis separabit.” (Who shall separate (us)?)

The Colonel’s Review is held seven days ahead of the Trooping the Colour parade which has marked the sovereign’s birthday for more than 260 years.

It remains unclear whether the princess, who is undergoing chemotherapy after a cancer diagnosis, will attend Trooping the Colour, a major fixture in the royal calendar.

She appealed for time, space and privacy for her family when she announced on March 22 she was being treated for an undisclosed form of cancer.

The Prince of Wales gave a positive update about his wife’s treatment during a visit to the Isles of Scilly earlier in May, saying “she’s doing well” when questioned by a hospital administrator.

The Irish Guards posted a video of the letter being read to the regiment on X saying: “The Irish Guards were deeply touched to receive a letter from our colonel, Her Royal Highness, the Princess of Wales this morning.

“We continue to wish Her Royal Highness well in her recovery and send her our very best wishes. Quis Separabit.”

The Regiment gave a round of applause after the letter was read out.

Kate will be represented at the Colonel’s Review by General James Bucknall, who will act as the chief inspecting officer of the day in the princess’ absence.

During the Trooping ceremony, held on Horse Guards Parade in Whitehall, it is understood the King will carry out the review of the Guardsmen and officers from an Ascot Landau carriage with the Queen.

The change from last year’s ceremony, where Charles inspected the troops on horseback, reflects earlier Buckingham Palace briefings where it was highlighted that each engagement by the King would be reviewed and adaptations made when advised by doctors.

Charles is likely to travel by carriage with the Queen during the traditional procession to and from Horse Guards Parade, and is expected to watch the Trooping ceremony seated on a dais, rather than on horseback.

The colour which will be “trooped” past the massed ranks of guardsmen and officers will be from Number 9 Company, Irish Guards.