Prince Philip is to spend a second night in hospital after being admitted as "a precautionary measure" it has been confirmed.
The 96-year-old has been undergoing treatment at King Edward VII Hospital in central London for an infection arising from a pre-existing condition.
A Buckingham Palace spokeswoman said The Duke of Edinburgh was in good spirits and that his hospital stay is "not a cause for serious concern."
Prince Philip turned 96 on 10 June. He accompanied the Queen at the Trooping the Colour on Saturday, but missed Royal Ascot and the State Opening of Parliament, where his place was taken by the Prince of Wales.
Earlier Prince Charles said his father was "getting better".
He recently announced that he was to retire from royal duties from autumn 2017. Philip is patron of 780 organisations, "with which he will continue to be associated", according to Buckingham Palace.
Philip still has a busy calendar of engagements to fulfil before he steps down, which includes hosting the King and Queen of Spain in July.