Camilla vis-à-vis William and Harry, informally

STEPMOM

Think of her role in the royal family tree—she’s not their birth mother but shares a last name with them now.

"Camilla vis-à-vis William and Harry" points to her role in relation to the two princes—she’s their stepmother, since she married their father, King Charles III. The clue adds "informally" to hint at the casual term "stepmom" instead of the formal "stepmother." The answer plays on the modern, shortened version of the word, which fits the crossword’s concise style.