The Princess of Wales pulled out of attending Royal Ascot on Wednesday as she continued to seek the right balance of public engagements after her treatment for cancer.
Catherine was said to be disappointed at not attending the race meeting with her husband and King Charles and Queen Camilla.
She has been making a gradual return to public duties since it was announced in January that she was in remission from cancer.
Her public appearances have increased in recent weeks and she has attended three high-profile events including trooping the colour, the annual Order of the Garter service and a visit to a Victoria and Albert Museum storage facility in London. But it is understood she is trying to find the right balance as she fully returns to public-facing engagements.
Racegoers had been hoping to see Catherine, after the Prince of Wales was named as one of the figures awarding race prizes during the second day of the meeting.
Ascot officials had announced in a carriage list that the princess was due to be in the second carriage in the royal procession, alongside William.
Less than half an hour later, Kensington Palace confirmed that Catherine would not be attending and Ascot published a revised carriage list.