Catherine, the Princess of Wales and wife of Prince William, canceled plans on Wednesday to attend the horse races at Royal Ascot, a last-minute withdrawal that raised questions about the state of her recovery from cancer.

Kensington Palace, where Catherine and William have their offices, confirmed that William would attend the races, a popular date on the calendar of royals, but would not be joined by Catherine, who has appeared more regularly in public since announcing last September that she had completed chemotherapy treatment for an undisclosed type of cancer. In January, Catherine said she was in remission.

The princess is “disappointed” not to be present, said a palace official, who spoke on condition of anonymity, citing palace protocol. He added that she needs to find the “right balance” when returning to public engagements.

On Saturday, Catherine took part in Trooping the Color, a ceremony that marks the birthday of the monarch, King Charles III. Her public appearances had become routine, though her schedule is not as busy as it was before her illness.

This is a developing story. Please check back for updates.