The Princess of Wales has pulled out from a planned attendance at Royal Ascot.
Catherine, who is making a gradual return to public life after her cancer diagnosis last year, is trying to find the right balance as she fully returns to public engagements, according to royal sources.
The princess was said to be disappointed to miss the sporting occasion in Berkshire, where she would have appeared in the carriage procession.
She was due to attend on Wednesday with her husband the Prince of Wales and King Charles and Queen Camilla.
Kensington Palace confirmed she would not be attending the races.
The King, Queen and Prince William arrived in the first carriage of the royal procession accompanied by Prince Saud bin Khalid Al Saud, a member of the royal family of Saudi Arabia.
Catherine and William had been due to arrive together in the second carriage with golfer Justin Rose and his wife, Kate Phillips. Prince William will be awarding race prizes during the second day of the meet.
The princess was last seen smiling and joking with other royals on Monday during the Order of the Garter service in Windsor.
Recently her public appearances have increased with attendances also at Trooping the Colour on Saturday and a visit to the V&A East Storehouse museum on 10 June.
Catherine revealed in January she is in remission from cancer after making an emotional return to the hospital where she received treatment.
She announced her diagnosis last March before she revealed in September she had completed her chemotherapy, saying: "Doing what I can to stay cancer free is now my focus."
Catherine did not attend Royal Ascot last year, saying at the time she had been "blown away" by the messages of support she had received since her diagnosis and had been "making good progress" but was "not out of the woods yet".
The event, one of the highlights of the summer social calendar, is taking place over five days at the Berkshire racecourse and is expected to draw more than 250,000 spectators.
The carriage procession the Royal Family make onto the racecourse signals the start of the day.
The procession is celebrating its 200th anniversary, a tradition begun during the reign of George IV in 1825 when the monarch was accompanied by the Duke of Wellington.
The King and Queen have continued Queen Elizabeth II's close association with the races. The late Queen owned and bred racehorses, with more than 20 Royal Ascot winners during her 70-year reign.
The King and Queen have taken on her stable of horses and enjoyed their first Royal Ascot winner in 2023 when their horse Desert Hero triumphed in the King George V Stakes.
They will be hoping for a winner with their horse Rainbows Edge, ridden by William Buick for trainers John and Thady Gosden, in the Kensington Palace Stakes (17:35 BST).
The Royal couple were out of luck with their runner on Tuesday – Reaching High finished ninth in the Ascot Stakes.