Buckingham Palace said the 99-year-old was sent to hospital "as a precautionary measure" on Tuesday evening. He was admitted to the King Edward VII Hospital in central London.
BBC reported that the duke had been "feeling unwell for a few days" but it was not a Covid-19 related illness. According to Reuters, Prince Philip travelled by car to hospital and it was not an emergency admission. He was thereafter admitted on his doctor's advice.
A royal source also told the BBC that the Duke was "in good spirits" in hospital, where he is expected to remain for a few more days. Prince Philip will turn 100 this June.
Queen Elizabeth, 94, remains at Windsor Castle, where the pair have been residing since the end of their summer vacation at their Balmoral estate in Scotland due to the outbreak of Britain's coronavirus pandemic. Both the Queen and Prince Philip received the Covid-19 vaccine last month.