Thousands of flag-waving fans gathered Monday to watch Paul McCartney, Elton John and other musical royalty celebrate Queen Elizabeth II with a Buckingham Palace concert featuring acts from throughout her 60-year-reign. But the joy was tempered by news that the queen's husband, Prince Philip, was hospitalized with a bladder infection.

Palace officials said the prince, who will turn 91 on Saturday, was taken to the King Edward VII Hospital in London from Windsor Castle on Monday as a precaution and will remain under observation for a few days.

"I hope he's OK," said McCartney, who was due to close the concert. "We all send our best wishes for a speedy recovery."

Despite Philip's illness, members of the royal family including Prince Charles, his wife Camilla, Duchess of Cornwall, and Princes William and Harry sat in a royal box to watch the show, performed on a specially erected stage outside the palace.

The queen was cheered as she arrived partway through the show, wearing a gold lame cocktail dress under a dark cape. It was decided before Philip's illness that she would only watch part of the concert.

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    Some 18,000 contest winners watched the show from an enclosed area, while a huge crowd stretched down the Mall, the wide boulevard leading up to the palace.

    The lineup featured a full hand of knights -- McCartney, John, Cliff Richard and Tom Jones, all "Sirs" -- along with Dame Shirley Bassey, Stevie Wonder and younger artists including JLS and Kylie Minogue.

    The show opened in a blaze of sound and color, as a scarlet-clad military band joined Robbie Williams onstage for his hit "Let Me Entertain You." Black Eyed Peas star Will.i.am performed "I Gotta Feeling" with songstress Jessie J.

    In true something-for-everyone mode, performances ranged from pianist Lang Lang playing Gershwin to American soprano Renee Fleming to 64-year-old Grace Jones hula-hooping her way through "Slave to the Rhythm."

    It was the veteran performers who went down best. The crowd roared along to Cliff Richard's "Congratulations," and cheered Bassey singing -- fittingly -- "Diamonds are Forever." Prince Harry could be seen singing along -- "Why, why why?" -- as Tom Jones sang "Delilah."

    Ska band Madness was expected to perform "Our House" on the palace roof, evoking a similar appearance at a Golden Jubilee concert 10 years ago by Brian May of Queen.

    Until Monday, Philip had been the queen's constant companion throughout the jubilee celebrations.

    He had joined the queen and senior royals on the River Thames in cold and blustery weather Sunday for a pageant in honor of Elizabeth's 60 years on the throne

    The prince, who married then-Princess Elizabeth in 1947, has cut back on official engagements in recent years but still maintains a busy schedule. He spent four nights in the hospital over Christmas after suffering chest pains and underwent a successful coronary stent procedure to clear a blocked artery.

    The palace said Philip was "understandably, disappointed about missing this evening's Diamond Jubilee Concert," as well as a St. Paul's Cathedral service and other jubilee events planned for Tuesday.

    The monarch's own musical tastes are a mystery, and the Press Association news agency reported she brought a pair of earplugs to a similar concert a decade ago. According to The Guardian newspaper, the only song the queen has ever been known to request is "Some Enchanted Evening" from the Rodgers and Hammerstein musical "South Pacific."

    "I don't think she's a big pop music fan," said Elton John, who paid tribute to the monarch's constancy.

    "She's not trendy, she doesn't follow any fads," John told the BBC. "She's stoic, she's brilliant, she's wise, she's funny, and we're all really happy to be here."

    Before the concert, 12,000 contest winners and charity workers enjoyed a jubilee concert in the palace grounds. Each received a hamper containing a meal -- partly created by experimental chef Heston Blumenthal -- of tea-smoked Scottish salmon, coronation chicken and strawberry crumble crunch made with fruit from the queen's Sandringham estate.

    The jubilee was being marked around the world in members of the 54-nation Commonwealth of former British colonies.

    The small Pacific island nation of Tonga claimed the honor of lighting the first of more than 4,200 commemorative beacons to be set alight in Britain and abroad. The queen will light the final beacon following the concert.

    One beacon will be lit in Kenya at the Treetops Hotel, where Elizabeth was informed of her father's death in 1952, making her the queen.

    Margaret Watson, 73, in the crowd near Buckingham Palace on Monday, remembered watching the Coronation on the television set which her family bought especially to watch the event.

    "I am here to say thank you to the queen for all she has done," said Watson, who came to London from Yorkshire in northern England with family members. "I am just so pleased to have lived through her reign."