"The Duke of Edinburgh has been admitted to King Edward VII Hospital for assessment and treatment for a chest infection," Buckingham Palace said on Friday.
Prince Philip, who was absent from the memorial service for Everest conqueror Edmund Hillary on Wednesday, has been feeling under the weather for several days and cancelled other engagements earlier this week due to a "heavy cold".
His condition worsened on Thursday and his doctor ordered him to hospital. However, according to reports, the 86-year-old is "up and about and dealing with his correspondence" in a private suite.
"His Royal Highness' programme of engagements for the weekend has been cancelled," added the palace spokesperson.
Prince Philip was in good health last weekend, as he took part in activities organised for the state visit of French President Nicolas Sarkozy and his wife Carla. And one of the Queen's physicians has described him as "astonishingly fit for a man of his age".
Her Majesty remains in Windsor Castle, where the pair have been residing over the Easter holiday period.