The Army has removed an announcement on its website that the Princess of Wales is reviewing Trooping the Colour in June after not seeking approval from Kensington Palace.
Tickets were being sold on the official website for the 8 June military spectacle, advertising an appearance by Kate.
However, according to the PA news agency, the event details were published because of Kate's role as Colonel of the Irish Guards, the regiment which is trooping its colour this year.
The Ministry of Defence's website also named the King as attending the main Trooping ceremony on June 15, also known as the Birthday Parade, because it marks the sovereign's official anniversary, with bookings being taken for a ballot for tickets.
The announcement caused confusion on Tuesday because there had been no official confirmation from Kensington Palace or Buckingham Palace.
King Charles has postponed all public-facing duties amid his ongoing cancer treatment, but did meet with Chancellor of the Exchequer Jeremy Hunt in-person at Buckingham Palace on Tuesday.
Meanwhile, the Princess of Wales is recuperating from abdominal surgery and is not expected to return to royal duties until after Easter.
© GettyKate, 42, has not been seen publicly since Christmas Day in Sandringham, Norfolk but was pictured by unauthorised paparazzi being driven close to her home in Windsor earlier this week.
In the image published by TMZ, the Princess was seen wearing sunglasses in the passenger seat of a car with her mother Carole Middleton driving.
© GettyIt comes after Kensington Palace addressed social media speculation over the royal's health last week.
A spokesperson for Kate said: "We were very clear from the outset that the Princess of Wales was out until after Easter and Kensington Palace would only be providing updates when something was significant."
Charles and Kate will miss the annual Commonwealth Day service at Westminster Abbey in London on Monday 11 March.
Queen Camilla and the Prince of Wales will lead the royals, including the Duke and Duchess of Edinburgh, the Princess Royal, the Duke and Duchess of Gloucester and the Duke of Kent.
