LONDON — Kate, the Princess of Wales, will miss a military ceremony she would usually take part in next month as she continues her cancer treatment, a Kensington Palace spokesperson said Thursday.

Bearing the honorary rank of Col. in Chief of the Irish Guards, Kate, 42, wife of the heir to the throne, Prince William, would normally be part of the ceremonial military event which takes place in London on June 8.

The princess has not been seen in public since she revealed she had cancer in…