Prince Philip has been taken to hospital as "a precautionary measure", Buckingham Palace have confirmed.
The 99-year-old was admitted to the King Edward VII private hospital in Marylebone after feeling unwell on Tuesday night.
A statement from the Palace said: "His Royal Highness The Duke of Edinburgh was admitted to the King Edward VII Hospital in London, on Tuesday evening.
"The Duke's admission is a precautionary measure, on the advice of His Royal Highness's Doctor, after feeling unwell.
"The Duke is expected to remain in hospital for a few days of observation and rest."
According to BBC News, the Duke of Edinburgh's illness is not thought to relate to coronavirus and his hospital admission was not an emergency.
Philip - the longest-lived male member of the Royal Family in history - is due to turn 100 in June.