The Princess of Wales has apologised for missing a Trooping of the Colour rehearsal in a letter to the Irish Guards.
Kate, who is undergoing cancer treatment, has confirmed that she will not be attending the event on Saturday, known as the Colonel’s Review.
As Colonel-in-Chief of the Irish Guards, she was due to be saluted in this role for the first time but is now set to sit out, and she may also miss next Saturday’s Trooping of the Colour.
In a letter to the guards, Kate wrote: “I wanted to let you know I am proud of representing the entire regiment ahead of the Colonel’s Review and Trooping of the Colour.
“I appreciate everyone trooping this year has been practising for months and dedicating many hours to ensuring their uniforms and drill are immaculate.
“Being your colonel remains a great honour and I am very sorry I will not be able to take the salute at this year’s Colonel’s Review.
“I hope I am able to represent you all very soon.”
Kate revealed her cancer diagnosis in a video message in March.
In recent weeks, she has been spending more time out and about with family.
The Irish Guards have responded to the Princess's letter, tweeting: “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.”
It remains unclear whether the princess, who is undergoing chemotherapy, will attend Trooping the Colour.
She has appealed for time, space and privacy for her family when she announced 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.
