LONDON - Each step has been rehearsed, each flower meticulously arranged, the aisle of Westminster Abbey transformed into a flowering avenue of trees.

With just hours to go before his wedding to Kate Middleton, dedicated royal watchers camped outside got an unexpected surprise - a visit from Prince William.

The 28-year-old groom-to-be emerged from his residence Thursday night to greet the hordes of well-wishers gathered along the processional route. Dressed in khakis and grinning broadly, William shook countless hands as his photo was snapped on cell phones and digital cameras.

The visit lent further excitement to the carnival atmosphere near the abbey, where hours earlier 29-year-old Kate had a final run-through with William's best man, Prince Harry.

A throng of curious tourists, dedicated monarchists, souvenir vendors, William-watchers and Harry-hunters have turned the Union Jack-bedecked streets into a scene of festive chaos.

"It's a once-in-a-lifetime thing. Not many kings-to-be are going to be married anytime soon," said 26-year-old Sarah White, camped out with her sister, Liz. "Everyone's making friends and is in good spirits - or at least will be until tomorrow."

The only clouds on the horizon: the threat of rain and the intrusion of politics, with the British government revoking an invitation to Syria's ambassador to condemn a deadly crackdown on protesters that has left hundreds dead.

Friday's ceremony has been planned like a military operation. More than 1,500 soldiers, sailors and air crew will be on duty to line the couple's procession route between the abbey and Buckingham Palace, just under a mile (1.6 kilometers) away.

An additional 5,000 uniformed and undercover police will be on alert for threats from Irish dissident terrorists, Muslim extremists, anti-monarchists, royal obsessives and drunken hooligans.

The royal nuptials will offer pomp and circumstance on a grand scale, starting with a global guest list of 1,900 that includes kings and queens, sports stars, music royalty, the couple's university chums, Royal Air Force pilots and charity workers, as well as friends and family.

Royal carriages drawn by mounted troops of the Household Calvary will roll to the palace in a sweeping procession under fluttering rows of Union Jacks. Hundreds of thousands are expected to line a parade route scrubbed clean in recent days.

Westminster Abbey itself has been remade into a blooming forest, with six field maples and two hornbeams lining the aisle to the altar.

William and Kate have been intimately involved in planning their wedding, officials say, from the music to the flowers to the cake - in fact, two cakes. Kate opted for a traditional white-iced fruitcake while William made sure that was accompanied by his childhood favorite, a chocolate biscuit cake.

Britain has not seen a royal celebration on this scale since 1981, when Prince Charles married Lady Diana Spencer at St. Paul's Cathedral.

Much is at stake for the royal family, who hope the latest match bolsters the Windsor dynasty, which has been buffeted by a series of failed marriages, including those of Charles and Diana, Prince Andrew and Sarah Ferguson, and Princess Anne and Mark Phillips.

Despite the tawdry way Charles and Diana's fairy tale ended - in a 1996 divorce after embarrassing admissions of adultery on both sides - most Britons feel an outpouring of goodwill for his son William and fiancee Kate.

The British government also hopes the wedding will lift people's spirits during a period of tough austerity measures. The Conservative-led government is cutting 81 billion pounds ($135 billion) in spending through 2015, slashing hundreds of thousands of government jobs and sharply hiking tuition fees.

Excitement built Thursday, as a crowd of die-hard fans camped out in tents and sleeping bags swelled near the 1,000-year-old abbey.

Among them was India Marlow-Prince, a 17-year-old from London who was picnicking with friends. The trio painted their faces with the Union Jack and wore tiaras and matching hot pink T-shirts with the homemade slogan "Will and Kate forever."

"She is the Diana of our generation. And Wills is a babe," Marlow-Prince said. "We are a little annoyed at her for taking him, but there's always Harry."

Prince Charles' wife Camilla, the duchess of Cornwall, delighted royal fans by emerging from her residence nearby.

"We're all ready for tomorrow," she said. "It's wonderful and we're all very excited."

More royal-watchers gathered outside the five-star Goring Hotel, where Kate and her family were spending her last night as a single woman. A canopy was erected over the entrance to block onlookers from catching sight of Kate when she emerges in her wedding gown Friday morning.

The dress has been the best-kept secret of this very public event. Its designer remains unconfirmed, and hundreds of millions of TV viewers will see it for the first time when Middleton steps out of her Rolls-Royce at the abbey. Her husband-to-be will get a first glimpse a few minutes later, when she makes her entrance.