On June 21, one of the largest assemblages of European royalty since Prince Charles's and Prince Andrew's weddings turned out for a very special occasion indeed: the "decade birthdays" party thrown by Queen Elizabeth for the Queen Mother, Princess Margaret and Princess Anne, who next month turn 100, 70 and 50, respectively, and for Prince Andrew, 40. The Queen Mum, clad in mint green, was the belle of the $150,000 black-tie ball ("She's always been a party girl," says Cleo Laine, a guest).
But most eyes were on a guest long absent from royal circles: the Duchess of York, invited by ex-husband Andrew. As the 900 attendees—among them King Juan Carlos and Queen Sofia of Spain and exiled King Constantine of Greece—filed into Windsor Castle, Fergie, 40, quietly used a side entrance. "She didn't want to seem as though she was milking the situation" for publicity, says a friend.
No less notable were the absentees. Prince William, who turned 18 that day, stayed at nearby Eton to cram for finals. Prince Harry, 15, was deemed too young for an event that did not start until 10 p.m. And Camilla Parker Bowles, 52, was not invited (though her ex-husband Andrew Parker Bowles, the Queen Mum's godson, was on hand). Encouraging as her brief meeting last month with the Queen may have been for Charles's paramour, "it is still 'slowly, slowly,' when it comes to the Queen," says royals reporter Peter Archer.
As the champagne flowed, however, the 74-year-old monarch chatted easily with Fergie, who wore a pink sequined gown by British designer Ben De Lisi. The duchess's daughters Princesses Beatrice, 11, and Eugenie, 10, "were very excited that their mother was heading off to Windsor," says a friend. (To partygoers' relief, there were no scenes with Prince Philip, 79, who reportedly holds his ex-daughter-in-law in low esteem.)
Dateless, Andrew danced with his ex at least once and kept an eye on her throughout the evening. "They are obviously devoted to one another," says Lord Palumbo, a guest. "I suppose it was a bit nerve-wracking for her, but she seemed relaxed."
As did the Queen, who kicked up her heels to the strains of Lester Lanin's 15-piece swing band. (Margaret was confined to a wheelchair with injured feet.) Meanwhile, in a nearby room done up as a disco, the younger set cut loose to the Rolling Stones' "Brown Sugar." Says a guest of the Queen: "She was grinning from ear to ear."
Though Charles took off early, the Queen and her mum grooved well past a 12:30 a.m. egg-and-sausage breakfast served by scarlet-jacketed servants. A musician marvels that around 3 a.m., when songwriter Tim Rice sang "It's All Over Now," "there were some 200 guests still partying."