The Duke of Edinburgh was absent from last night's Diamond Jubilee concert and will miss today's state procession after being admitted to hospital with a bladder infection.
Prince Philip, 90, was taken to the King Edward VII Hospital in London from Windsor Castle yesterday as a precautionary measure, and will be kept in for observation for a few days, according to Buckingham Palace.
Medical experts have suggested the Duke could have developed the condition during Sunday's Diamond Jubilee pageant, when he stood for hours facing torrential rain. Vinod Nargund, consultant urological surgeon at Homerton University Hospital, said the stressful conditions of the flotilla could have contributed to an infection.
"Stress is one of the predisposing factors," he said. "For example, if you work for three or four nights in a row, you will be more prone to infection because your immunity will be reduced."
The Queen's reign of 60 years was marked by 4,000 beacons lit across the Commonwealth, 12,000 people picnicking in the palace gardens, and four musical knights among the performers at last night's royal concert.
Sir Paul McCartney, Sir Cliff Richard, Sir Tom Jones and Sir Elton John were among the stars at the Buckingham Palace concert. Sir Paul, who closed the concert with four songs, wished the Duke well, saying: "We all send our best wishes for a speedy recovery."
Kylie Minogue brought her Aussie-commoner credentials to what some were calling "the people's pop pageant".
The extensive weekend security operation mounted by the Metropolitan Police will continue today with the official parade from Westminster, up Whitehall and along the Mall. Only 10 arrests were made by the Met in London in connection with the celebrations on Sunday.
With the bank-holiday downpour still dominating the thoughts of tens of thousands of tourists and celebrating monarchists, the forecast for cloudless skies last night was enough to cheer up Chris Whittington, from Hornchurch, Essex. "I've run out of dry clothes, my sleeping bag is soaked through, and my tent is ruined. But apart from that it's been excellent," he said.
By the time a convoy of eight lorries arrived at the palace yesterday morning, holding the jubilee picnic packs specially created by Heston Blumenthal, the torrential rain had eased off.
For Bruno Peek, the Queen's pageant master, the operation to light beacons across the UK and throughout the Commonwealth, leading to the last beacon being lit by the Queen herself last night, was the highlight of the celebrations.
The first beacon was in Marlborough, New Zealand. Blazes followed in Tonga, Malta and Kenya. In Australia, the Prime Minister, Julia Gillard, took the honour in Canberra.
In the UK, the network of beacons crossed the country, linking landmarks across Scotland, England, Wales and Northern Ireland.