Princess Kate is apologizing for missing an event honoring her father-in-law King Charles III amid her cancer diagnosis.

The Irish Guards, a regiment of the British army, shared a letter sent by Princess Kate on X on Saturday where she wrote that she was proud of "the entire regiment ahead of the Colonel's Review and Trooping of the Colour."

"I appreciate everyone trooping this year has been practicing for months, and dedicating many hours to ensuring their uniforms and drill are immaculate," she continued in the letter shared to social media.

Saturday marks the final rehearsal for Trooping the Colour.

While the event, which is slated for July 15, is a ceremonial tradition and celebration of King Charles III, the monarch celebrates his actual birthday on November 14.

Need a break? Play the USA TODAY Daily Crossword Puzzle.

"Being your colonel remains a great honor and I am very sorry that I'm unable to take the salute at this year's Colonel's Review. Please pass my apologies to the whole Regiment, however I do hope that I am able to represent you all once again very soon," she added in the letter. "Please send my very best wishes and good luck to all involved."

Princess Kate is currently undergoing treatment for cancer and last month, Kensington Palace told The Evening Standard and BBC that the princess has not returned to work yet.

Princess Kate apologizes for 'editing'photo of family pulled by image agencies

It's been a hectic year for the Royal Family in Britain. Princess Kate underwent a planned abdominal surgery Jan. 16 and then remained out of the public eye. Two months later, she resurfaced in a public video, announcing she had been diagnosed with cancer and would undergo "a course of preventive chemotherapy treatment."

"I wanted to take the opportunity to thank you personally for all the wonderful messages of support and for your understanding whilst I've been recovering from surgery," Kate says in a video released by the palace. "It has been an incredibly tough couple of months for our entire family. But I've had a fantastic medical team who've taken great care of me, for which I'm so grateful."