The Duke of Edinburgh has been taken to a hospital as a precautionary measure for a bladder infection.
According to palace officials, the Duke of Edinburgh was taken by ambulance from Windsor Castle to King Edward VII hospital in London.
The prince, who turns 91 next week, has been placed under observation and is expected to remain there for several days.
On Sunday, the prince and other members of the royal family spent several hours standing as the large river pageant sailed down the Thames , amid rain squalls and blustery conditions.
Buckingham Palace officials have not revealed if the prince's illness was connected with his exposure to the damp and chilly weather.
"Both the Queen and Prince Philip are stoic people of their generation," Sky's royal commentator Alastair Bruce said.
"Watching them stand in the rain on Sunday, determined to look everybody in the eye, was wonderful to see and I am sorry to see he won't be able to do the rest of the jubilee celebrations.
The ambulance service in Berkshire received a call from the castle at about 2pm on Monday.
Last October, uncharacteristic cold weather forced him to pull out of an overnight stay in Italy for the launch of the ARC Green Pilgrimage Network.
He had just completed a busy 11-day official royal tour to Australia with the Queen that saw them visit Perth, Melbourne, Canberra and Brisbane.
Then in December the prince was rushed from the Sandringham estate to hospital in Cambridgeshire after suffering chest pains.
The monarch travelled by helicopter to near Papworth Hospital on Christmas Eve and visited her husband in the cardiothoracic unit, where he was treated for a blocked coronary artery.
The announcement of the duke's latest hospital stay was made just hours before the start of the Queen's Jubilee Concert at Buckingham Palace , in front of thousands of fans.
In St James's Park retired teacher Kate Gregory, 62, from Stourbridge in the West Midlands, said: "I feel sorry for the Queen really that it has happened now, because he's always by her side.
"It is not going to be easy for her. We wish him all the best and hope he is
Bruce added: "He will be so angry he is not here with everybody else for the concert.
"But I would imagine he would insist that show must go on."
Meanwhile a palace spokesman said: "He is, understandably, disappointed about missing this evening's Diamond Jubilee Concert and (Tuesday's) engagements ."