A spokesperson said the 96-year-old is being treated for an infection
Prince Philip has been taken to hospital as a "precautionary measure" for treatment of an infection, Buckingham Palace has said.
In a statement quoted by The Guardian, a spokesperson 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."
The 96-year-old royal, who has had some medical problems in recent years, appeared to be in good health at Ascot racecourse with the Queen on Tuesday.
The royal couple were joined at the sporting and social occasion by other senior members of the Royal family, including Prince Charles and Prince William.
Prince Philip was due to attend the racecourse again today.
The hospitalisation comes as Queen Elizabeth is set to formally commence the new British parliament this morning with the traditional Queen's Speech.
Prince Philip is said to be 'disappointed' to be missing today's events, but is otherwise in 'good spirits'.
Last month, Prince Philip announced he will give up his public duties from the autumn.