Prince Philip travelled from Norfolk to King Edward VII’s Hospital in London for a “planned admission” on Friday morning.
Royal reporter Victoria Murphy tweeted that the Duke of Edinburgh’s admission was planned as a “precautionary measure” for observation and treatment related to a preexisting condition.
She added later that the Duke “walked into the hospital.”
The prince, 98, retired from royal duties in August 2017 after spending decades supporting Queen Elizabeth II, his wife of 72 years.
He was in a serious car crash in early 2019 in which he flipped his car.
It was announced in February by the Crown Prosecution Service that he wouldn’t face any charges as a result of the crash.
Members of the Royal Family are expected to make their public appearance in Sandringham after church on Christmas morning.
Prince Philip did not join them for last year’s appearance.