Kate, the Princess of Wales, underwent planned abdominal surgery and will remain in hospital for 10 to 14 days, Kensington Palace said.
The princess was admitted to The London Clinic on Tuesday for the procedure.
The operation was successful and she will return home after the two-week period to continue her recovery.
She is unlikely to return to public duties until after Easter.
King Charles III will also be admitted to hospital next week for treatment on his prostate, meaning his public engagements will be postponed, Buckingham Palace said
The Palace refused to confirm what Kate was being treated for but confirmed that the condition was non-cancerous.
“The surgery was successful and it is expected that she will remain in hospital for 10 to 14 days, before returning home to continue her recovery," Kensington Palace said.
"Based on the current medical advice, she is unlikely to return to public duties until after Easter.
“The Princess of Wales appreciates the interest this statement will generate. She hopes that the public will understand her desire to maintain as much normality for her children as possible; and her wish that her personal medical information remains private.
“Kensington Palace will, therefore, only provide updates on her royal highness’s progress when there is significant new information to share.
Catherine Princess of Wales through the years - in pictures
“The Princess of Wales wishes to apologise to all those concerned for the fact that she has to postpone her upcoming engagements. She looks forward to reinstating as many as possible, as soon as possible.”
The Prince and Princess of Wales have solidified their position as being among the most popular members of the royal family since Prince Harry and Meghan’s stormy departure to California in 2020.
The princess, in particular, is a reliable royal in the public eye and is increasingly undertaking solo public engagements.
Her last public appearance was the annual Christmas Day service at Sandringham.
The princess, who celebrated her 42nd birthday earlier this month, met and began dating Prince William, 41, now the Prince of Wales, at St Andrews University, and married him in Westminster Abbey in 2011, becoming the Duchess of Cambridge and also a future queen.
The mother of three missed out on a trip to Singapore with her husband last autumn for the Earthshot Prize awards, staying at home with 10-year-old son Prince George.
The couple did not embark on a joint official overseas tour in 2023, taking a back seat to allow King Charles and Queen Camilla to embark on their inaugural travels.
They are reportedly planning to travel to Italy this spring.
