The Duke of Edinburgh is being looked after “very well” in hospital, the Prince of Wales said on Monday.
Prince Philip, 98, has spent a third night at King Edward VII’s Hospital in central London for treatment for a “pre-existing condition”.
The duke’s planned admission on Friday to the private central London hospital was described as a “precautionary measure” by Buckingham Palace.
During a visit to flood-hit communities in South Yorkshire, Philip’s eldest son was asked about his father’s health by a reporter.
“He’s being looked after very well in hospital,” Charles replied.
“At the moment that’s all we know.”
During a visit to Fishlake, which was devastated by floods brought on by heavy rains after the nearby River Don burst its banks, a woman asked Charles: "Sir, how is your father?", according to The Telegraph.
He replied: "Alright. When you get to that age things don't work so well."
The Queen did not change her schedule as a result of her husband’s hospital stay.
She left Buckingham Palace for Norfolk by train on Friday to begin her traditional festive break at her private Sandringham estate, where the duke spends much of his time since retiring from public duties.
On Sunday the Queen attended church, accompanied by the Countess of Wessex.
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The duke, who turned 98 in June, has generally enjoyed good health, and appeared to recover well from a planned hip replacement operation in April 2018.
Philip escaped with minor injuries after a dramatic car crash near Sandringham in January, but in the past decade has been admitted to hospital for abdominal surgery, bladder infections and a blocked coronary artery.
A Buckingham Palace statement on Friday said: “The Duke of Edinburgh travelled from Norfolk this morning to the King Edward VII Hospital in London for observation and treatment in relation to a pre-existing condition.
“The admission is a precautionary measure, on the advice of His Royal Highness’s doctor.”
The duke was not taken by ambulance and was expected to be in hospital for a few days.
Philip is known for his “no fuss” approach and is unlikely to receive many visitors while he is being treated at the hospital.
Buckingham Palace would not go into details about Philip’s pre-existing condition, or the nature of his treatment, but there is likely to be concern for the duke among well-wishers, given his age.
Philip’s decision to retire from public duties during 2017 was not health-related, Buckingham Palace said at the time of the announcement.
The duke is an advocate of healthy eating combined with exercise. He once said he more or less followed the Atkins diet and he drinks only moderately.
He has given up riding carriages competitively, but earlier this year was photographed in the grounds of Windsor Castle holding the reins as he guided a horse and carriage through the estate.