In fact, he actually increased his public appearances, going past his sister Anne to the number one spot:
But this year, Princess Anne has dropped to second place, though she was out and about even more in 2025, according to the list published by The Daily Mirror. The article, by Russell Myers and Jennifer Newton, based on Trebles research with data up until December 18th, reveals that although the 75-year-old had 478 engagements, she was outpaced by her brother, 77-year-old King Charles. He carried out 532 official acts, netting him this crown in addition to that other one. [On the list published on December 31st by Treble, the total number adds to 533, as the King conducted one more engagement on December 19th].
That uptick in activity can be viewed as a sign that his health is indeed improving, a theory bolstered by an announcement the king made earlier this month. Thanks to early diagnosis, effective intervention, and adherence to doctors orders, my own schedule of cancer treatment can be reduced in the new year, the king said in a prerecorded message that aired as part of Stand Up to Cancers 2025 broadcast on the UK network Channel 4. This milestone is both a personal blessing and a testimony to the remarkable advances that have been made in cancer care in recent years.
https://www.vanityfair.com/style/story/king-charles-princess-anne-kate-middleton-hardest-working-royals
So it probably wouldn't seem a very believable excuse ("sorry, I'm washing my hair that week" ). While that would make it funnier, it also, realistically, makes it less likely he'd use it.