Kate Middleton sends letter of apology for missing King Charles' birthday parade rehearsal

Kate Middleton apologized this week for missing the rehearsal for King Charles' annual birthday parade as she continues to undergo treatment for cancer.

The Irish Guards, who are leading Trooping the Color this year, said in a tweet they were “deeply touched” by the letter they received Saturday morning from the Princess of Wales, 42, who serves as their honorary colonel and would have traditionally participated in this weekend's Colonel's Review.

“I wanted to write to you and let you know how proud I am of the entire regiment before the Colonel's Review and Color Parade,” Middleton wrote. “I appreciate that everyone participating this year has been training for months and putting in many hours to ensure their uniforms and drills are impeccable.”

Noting that she considers her position as colonel “a great honor,” Middleton said she was “very sorry that I could not [to] take the salute at this year's Colonel's Review.

“Please pass on my apologies to the entire regiment, but I hope to be able to represent you again very soon,” she wrote.

The Princess in her letter and the Irish Guards in their tweet signed the regiment's motto, “Quis Separabit” – a Latin phrase taken from the Order of St. Patrick which translates to “Who will separate us?”

The letter comes just over a week after Kensington Palace confirmed that the princess would not take part in the Colonel's Review ahead of the parade scheduled for June 15.

Middleton would normally be a major part of Trooping the Color, the annual military exhibition marking the sovereign's official birthday.

After undergoing successful abdominal surgery in January, Kensington Palace announced that Middleton would likely refrain from public service until after Easter. Speculation about the royal's health quickly followed, especially as her hospitalization overlapped with that of the 75-year-old king, who announced his cancer diagnosis shortly after.

In March, the Princess of Wales confirmed that she too had been diagnosed with cancer and was undergoing preventative chemotherapy.

A palace spokesperson told the BBC last month that Middleton “is not expected to return to work until cleared by her medical team.”