According to Express, Charles was again approached by another concerned citizen in Fishlake, who asked him: "Sir, how is your father?"
He replied: "Alright. When you get to that age things don't work so well."
Prince Philip spent a third night in hospital for treatment relating to a "pre-existing condition", which has been described by Buckingham Palace as a “precautionary measure”.
In a statement, the palace 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.”
According to Mail Online, Philip has also been "battling a flu-like illness for weeks" and suffered a fall before being rushed to hospital.
Speaking about the Duke’s health in recent months, one source told the publication: “The Duke has had a bad turn recently and has been looking much frailer of late.
“He's a remarkable man who has always prided himself on how robust he is, but he is six months off his 99th birthday and age takes its toll.
“He hasn't been looking terribly well of late,” the royal insider said.