Kate, wife of heir to the throne Prince William, was expected to sit in the Royal Box at Centre Court during the championship match between Novak Djokovic and Carlos Alcaraz on Sunday.
Since 2016, the princess has been the patron of the club that hosts the annual grass-court Grand Slam tournament.
Her ceremonial duties include handing out the winner’s trophies after the singles finals, although she was not on hand on Saturday when Barbora Krejcikova defeated Jasmine Paolini for the women’s title.
Kate revealed in March that she has cancer and was undergoing chemotherapy.
Her lone public appearance since then was attending last month’s birthday parade for King Charles III.
Before that event, she released a statement saying she was “making good progress” but still had “good days and bad days”.
Prince William has been a regular at Wimbledon finals but was not going to be there on Sunday.
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Instead, he planned to go watch England face Spain in the final of the men’s soccer European Championship in Germany. He is the president of the English Football Association.
Queen Camilla, wife of King Charles III, visited Wimbledon on Wednesday.