Prince Philip, the 96-year-old husband of the Queen, has been admitted to hospital with an infection and as a result has missed the formal state opening of Parliament.
The Duke of Edinburgh remains in 'good spirits,' Buckingham Palace said.
'The Duke of Edinburgh was admitted to King Edward VII Hospital in London last night, as a precautionary measure, for treatment of an infection arising from a pre-existing condition,' a spokesperson for the Palace said.
'Prince Philip is in good spirits and is disappointed to be missing the State Opening of Parliament and Royal Ascot.'
The Queen, the world's longest-reigning living monarch, celebrated her 91st birthday in April. She was accompanied in Parliament by her son, Prince Charles, who is heir to the throne,
When Philip announced in May that he would retire later this year from active public life, he quipped about not being able to 'stand up much'.
The Queen and Philip, who married at Westminster Abbey in 1947, are due to celebrate their platinum, or 70th, wedding anniversary in November.
Both the Queen and Philip have suffered some health issues in recent years.
The Queen missed a traditional Christmas church service last year for the first time in decades because of a heavy cold and was hospitalised in March 2013 with symptoms of gastroenteritis.
Philip underwent 'an exploratory operation following abdominal investigations' in 2013.
Additional reporting by Reuters.
