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.
More about the Royals
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.Slideshow: Royal fans flock the streets of London (on this page)
"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 away.Slideshow: Westminster Abbey: 1,000 years of history (on this page)
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.
3 planned to behead effigies
Metropolitan Police said three people planning to behead effigies at the royal wedding were detained in Brockley, southeast London, Thursday night on suspicion of conspiracy to cause public nuisance and breach of the peace.
Police said two men, ages 68 and 45, and a 60-year-old woman remained in custody at a local police station overnight.
A large guillotine was seized. Police said the trio planned to use it to cut the heads off the effigies.
The older man arrested was identified by Press Association as Chris Knight, head of the anti-royal anarchist group The Government of the Dead.
Nineteen other arrests, not specifically related to Friday's wedding, also were made in London earlier in the day.
Officers had warned of pre-emptive arrests on the eve of the big day.
Scotland Yard, which has vowed to deal "robustly" with suspected troublemakers, is believed to be concerned about activities by anarchist groups, Press Association said.
Grand wedding plans
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."Slideshow: Pre-nuptial prep for royal wedding (on this page)
More royal-watchers gathered nearby outside the five-star Goring Hotel, where Kate and her family are 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 dress 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.
After the ceremony
After Friday morning's ceremony, the couple will travel by carriage to the palace and emerge onto the balcony for a precisely timed kiss — at 1:25 p.m., or 8:25 a.m. ET — followed by a ceremonial fly-past of military aircraft.
Then the partying starts. Some 650 people are invited to a luncheon with the queen, and later that night 300 close friends and family will attend a black-tie evening bash.
The palace says Queen Elizabeth II and her husband Prince Philip planned to go away for the evening, leaving the younger royals free to party unfettered — and Harry to make his best man's speech away from his octogenarian grandparents' ears.
British singer Ellie Goulding, 24, is reportedly going to perform , and rumors have it that Harry has even planned a morning breakfast for those with the stamina to dance all night.
Hundreds of thousands of people across the country will celebrate as well, for the day has been declared a public holiday. Over 5,500 official street parties are planned, including one by the anti-monarchist group Republic and another on Downing Street, home to Prime Minister David Cameron.
Cameron said the wedding will bring "happiness and joy and light relief after some difficult times."Video: PM Cameron recalls camping out for Charles and Di
In William and Kate's wedding program, released Thursday and on sale for about $3, the couple said they have been deeply touched by the outpouring of affection toward them.
"We are both so delighted that you are able to join us in celebrating what we hope will be one of the happiest days of our lives," they wrote. "The affection shown to us by so many people during our engagement has been incredibly moving, and has touched us both deeply."
They also released a new photograph by celebrity photographer Mario Testino — a warm black-and-white image showing them with broad smiles and sparkling teeth.
Middleton will not promise to "obey" her new husband in her vows but instead to "love, comfort, honor and keep" him. She will walk up the aisle to the sounds of "I was glad," the anthem setting of Psalm 122 composed by Sir Charles Hubert Hastings Parry for the coronation of King Edward VII in 1902. The anthem was also sung at the 1981 wedding of William's parents.Video: Fans, near and far, gather for royals’ nuptials (on this page)
She will walk up the aisle to the sounds of "I was glad," the anthem setting of Psalm 122 composed by Sir Charles Hubert Hastings Parry for the coronation of King Edward VII in 1902. The anthem was also sung at the 1981 wedding of William's parents.
But as wedding excitement heated up, the weather in London cooled down. Royal wedding fans may want to pack extra umbrellas.
Gray skies were forecast for Friday, with a 30 percent chance of rain at the time of the ceremony, the Meteorological Office said. Some sunshine might break through in the morning, with temperatures rising to about 66 degrees.
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