Princess Kate commented on her absence from public life for the first time since announcing her cancer, in a letter to a British army regiment.

King Charles III’s birthday parade, Trooping the Colour, is due to take place in London next Saturday, June 15, and the British Army today conducted a rehearsal, known as the Colonel’s Review.

The Princess of Wales was originally slated to play a key role in the event but pulled out as she continues chemotherapy for cancer.

So she wrote a letter—signed off “Colonel Catherine”—in which she apologized for missing the occasion and praised the troops for their work preparing, while Kensington Palace said she is continuing her recovery at home.

In the letter, Kate wrote: “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 at Trooping the Colour this year has been practising for months and dedicating many hours to ensure their uniforms and drill are immaculate.

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

“Please pass on my apologies to the whole regiment. I do hope that I’m able to represent you all once again very soon. Please send my very best wishes and good luck to all involved.”