Princess Kate of Wales apologized for not attending final rehearsals on Saturday ahead of the Trooping the Colour parade in honor of the king’s birthday.

Kate, who is honorary colonel of the Irish Guards, wished the regiment all the best in its recovery from cancer.

“It is a great honour to be your Colonel and I am very sorry that I will be unable to take the salute at this year’s Colonels Review,” he wrote in the letter, shared by the Irish Guards on social media platform X. “Please extend my apologies to the whole regiment, although I hope to be able to represent you all once again very soon.”

The review is a dress rehearsal for the annual military parade held every June to mark the monarch’s official birthday. King Charles III will oversee the ceremony on June 15.

It is still unclear whether Kate will attend next weekend’s ceremony. She is undergoing chemotherapy treatment for an undisclosed type of cancer, which she announced in March, sparking speculation on social media about her health as she had not been seen in public for several months. She has given little information about her illness, which she says was discovered after major abdominal surgery.

The king is also undergoing treatment for cancer but has resumed public duties. He attended ceremonies this week marking the 80th anniversary of D-Day, the invasion of Nazi-occupied Europe on June 6, 1944.

Trooping the Colour is a 260-year-old tradition in which soldiers in full dress uniform parade before the King with their ceremonial flag, also known as their “colour”.

Charles is expected to attend the ceremony in a carriage with Queen Camilla and is expected to watch the ceremony from a dais, as he did on horseback last year.

On Saturday around 8,000 people watched the Irish Guards march down Horse Guards Parade in central London, dressed in bright red tunics and bearskin hats.

The military band played the national anthem and 240 horses marched in practice, including the regiment’s mascot, an Irish wolfhound named Seamus, who was dressed in a red cape and led across the square by his handler.

The incident, which occurred on a sunny but cool day, was a far cry from last year’s, when at least three security personnel fell unconscious in the scorching heat.

The Irish Guards said on Christmas Day they were deeply moved by Kate’s letter and wished her a speedy recovery.

Kate will take over from her husband Prince William as colonel of the regiment in 2022, as Prince William has been appointed colonel of the Welsh Guards.