The Duke of Edinburgh was admitted to hospital on Monday, forcing him to miss the Buckingham Palace concert in honour of the Queen's diamond jubilee and the other events planned for the close of the long weekend of celebrations on Tuesday.
He was taken to hospital just hours before the concert, which was opened by Robbie Williams and featured music from every decade of her reign.
The palace said the duke had a bladder infection and had been taken from Windsor Castle to the King Edward VII hospital in central London, the facility favoured by the royal family. In a statement, it said it was a precautionary measure and the duke was disappointed at not being able to attend the concert. He is expected to be kept in for observation for several days.
Philip, who is 91 on Sunday, had joined his family on the royal barge during the Thames diamond jubilee river pageant. Though he and the Queen, who is 86, stood for 80 minutes in the cold and rain, he did not then appear to be in discomfort.
His illness will undoubtedly cast a shadow over the bank holiday jubilee festivities for the Queen, who has referred to him as "my strength and my stay".
As is her right, the Queen was not in the royal box when the concert, staged around the Queen Victoria Memorial outside Buckingham Palace, opened with Robbie Williams belting out Let Me Entertain You to the 12,000 who won tickets in a ballot for the spectacular. Ducks took flight as fireworks and drums kicked off the show. David Cameron and his wife, Samantha, were among guests in the royal box.
So many people descended on St James's Park, next to Buckingham Palace, to watch the concert on a big screen that police officers declared the park full and diverted the overflow to Hyde Park. Organisers estimated crowds at 250,000 in the Mall, St James's Park and Hyde Park.
One of the show's most bizarre performances came from Grace Jones, who performed the whole of her hit Slave to Rhythm while hula hooping. Slightly misunderstanding the occasion, she left the stage shouting, "We love you, happy birthday our Queen."
The subject of the enthusiasm arrived late and equipped with earplugs, understandable for an elderly monarch not overly fond of rock and pop. She wore a heavy dark cape to keep warm.
Prince Harry did not take to the stage to reprise his role as the "tambourine man" in Sing, the jubilee No 1 hit jointly written by Gary Barlow and Andrew Lloyd Webber. A disappointment for the crowd, perhaps, but no one was going risk him outshining his grandmother on the night.
In the royal box Princess Anne and the Archbishop of Canterbury, Rowan Williams ,could be seen singing along gustily with Rolf Harris's rendition of Two Little Boys.
Among the lineup were three pop knights, Sir Cliff Richard, Sir Elton John and Sir Paul McCartney. Madness were there too, performing Our House from the palace roof.
Jessie J and JLS might not be such familiar figures to the Queen, but certainly were to her grandchildren, who were rocking in the royal box.
John wished the duke a speedy recovery and joked that his illness might be a ruse. "He hates pop music," he said of the confirmed Cole Porter fan. "Anything to get out of a pop concert."
The Prince of Wales acknowledged his father's absence in an emotional tribute on stage as the concert ended. "The only sad thing about this evening is that my father cannot be here with us because unfortunately he's been taken unwell," he said. "Ladies and gentlemen, if we shout loud enough he might just hear us in hospital," he added, as the crowd broke into the most deafening roar of the evening, then chanted "Philip, Philip, Philip" as the Queen was visibly moved.
Standing a few feet from his mother, Charles turned to her. "Your Majesty. Mummy," he said, just as he had addressed her on her golden jubilee. "A diamond jubilee is a unique and special event, some of us have had the joy of celebrating three jubilees with you, and I have the medals to prove it. And we're now celebrating the life and service of a very special person, over the last 60 years."
He added, to huge cheers: "So, as a nation is this our opportunity to thank you and my father for always being there for us. For inspiring us with your selfless duty and service and for making us proud to be British."
As the concert ended, the Queen removed the cape that had been keeping her warm to reveal a gold cocktail dress, trimmed with antique gold lace and adorned with Swarovsky crystals. One moment organisers will have been relieved not to relive was when, in 1977, the Queen stood torch in hand ready to light her silver jubilee beacon – and exclaimed: "Look, look. It's lit already." Which it was, having been prematurely ignited by an over-eager squaddie.
However, after watching a dazzling pyrotechnic and son et lumière, which enveloped the palace, she lit the national beacon in the Mall, the last of more than 4,200 jubilee beacons criss-crossing the UK and the world, drawing the day of celebrations to a close.
Crowds had gathered throughout the day. By 6pm, the grey clouds that had hovered over London for more than an hour parted to disclose a patch of hazy blue sky above Hyde Park and the air filled with the popping of corks and the smell of not-so-cheap burgers. There was a festival atmosphere, but it was more village fete than Glastonbury: folding chairs and Pimm's rather than rugs and cider.
An ironic cheer went up in the park as the rain began to fall, an hour before the concert began. But it was the news that the duke had been taken into hospital that did more to dampen spirits.
"The Queen will be a bit sad but she'll have her family around her and the crowds behind her. Everyone will be praying for him," said Phil Oke from Cornwall, clad in union flag trousers, top hat and waistcoat. His wife, Jenny, feared the news would upset the Queen.
"It will ruin it for her; they do everything together. It's so sad."
