As the sun rose over Prince William's home, crowds were already gathered outside to wish him luck on his wedding day.
The Prince spent his final night as a single man in his London home Clarence House with his father the Prince of Wales, stepmother the Duchess of Cornwall and brother Prince Harry.
By 6am thousands of royal fans were lining the Mall outside his historic residence, many of whom had camped overnight to ensure a good view of the wedding procession.
Last night William surprised fans with an impromptu walkabout on the famous throroughfare, spending several minutes shaking hands and thanking people for their support.
Friends Sue Heppell, 59, Susie Record, 67, and Ann Burch, 65, travelled from Newcastle to find a good spot outside Clarence House at midday yesterday.
Mrs Record said she had met William last night and he had seemed very relaxed about his impending nuptials.
"He asked us whether we were sleeping out," she said. "He didn't seem surprised."
The trio, who slept in foil sleeping bags in camping chairs, also saw David Cameron wander the Mall shaking hands last night, describing the reaction to his appearance as a "stampede".
Mrs Heppell said she was an ardent royalist, adding: "We think William and Kate are absolutely lovely people and just want to support them and want to experience all the atmosphere."
Another hardy royalist, Christina Laukenmann, from near Stuttgart, Germany, slept on the pavement on her own last night.
The 25-year-old, who is studying English in London, said: "I want to feel the atmosphere. There is no Royal Family in Germany so for me it's very special."
Spectators were already five-deep behind barriers along the famous thoroughfare hours before William and his best man Harry were set to leave Clarence House for Westminster Abbey.
Many well-wishers wore furry hats, tiaras and headbands and nearly all of them carried Union flags. There was a party atmosphere, with crowds cheering any cleaning vehicle driving past.
William and Kate Middleton will start their married life in Clarence House after they return from their honeymoon. The building is attached to St James's Palace and has been the home of royalty for more than 170 years.
For nearly half a century, it was home to the Queen Mother, who moved there with Princess Margaret in 1953.
Charles made the four-storey house his official London residence following his grandmother's death in 2002. He has lived there before, between the ages of one and three, when the residence was briefly home to his mother the Queen and father the Duke of Edinburgh after they were married in 1947.
Well-wishers lining the Mall outside Stable Yard Road, which leads to Clarence House, are set to be treated to a spectacular procession before the wedding.
William, wearing a dashing scarlet uniform, will be accompanied by Harry as they ride to the abbey in a chauffeur-driven Bentley limousine. The 6.22 metre-long State Car will ensure the brothers arrive some 45 minutes before the bride-to-be.
Onlookers on the Mall will then wave to Charles and Camilla when they leave Clarence House half an hour later, with the Queen and Philip set to leave Buckingham Palace moments after their departure.
But the crowd will ultimately be craning their necks to see the beautiful bride-to-be, who will be accompanied by her father Michael Middleton as they make their journey from the Goring Hotel to the abbey in a Rolls Royce Phantom VI.
Tents littered the length of the barriers and were scattered around St James's Park behind the Mall. There was a festival feel as well-wishers cleaned their teeth using bottles of water and queued outside rows of portable toilets.
Some of the crowd burst into a rendition of Rule Britannia as they waited for the first glimpse of William.
A group of female students from University College London wore charity shop wedding dresses.
One of them, Sophie Foan, 19, from Devon, said: "We thought it would be fun. We thought we'd keep an eye out for Harry as well."
She said they had taken care not to upstage the bride by wearing boots and suspenders under their dresses.
Friends Kathleen Little, 64, and Hazel Twyman, 62, from Fareham, Hampshire, camped in a tent last night to get a good spot.
Mrs Little said: "It was very cold and very hard on the bottom. But it was a lot of fun and this was the one thing I wanted to do before I die."
She said she had seen William and Harry last night, adding: "They looked very cool and confident."
Friends Margaret Bamber, 69, and Anne Johnson, 65, from Preston, Lancashire, arrived in The Mall at 10am yesterday.
The royalists said they had camped out previously for the Duke of York's wedding to Sarah Ferguson in 1986, as well as the Queen Mother's 100th birthday.
Jeanette Mann, 67, travelled from Southland, New Zealand, for the wedding celebrations.
"As soon as I heard the date, we got on the phone and booked a flight and hotel," she said. Mrs Mann slept in a chair by the barrier last night so she could get a good view of the princes.
She praised William for his support to New Zealanders after the devastating Christchurch earthquake and said his visit had meant so much to the families of those killed.
Sarah Gracey, 18, from near Vancouver, Canada, also camped out with her mother Maxine. Miss Gracey said it was her first trip to the UK.
"I'm mostly looking forward to the whole shebang. Where we're standing is perfect as we not only get to see Kate but the whole Royal Family and the horses and carriages," she said.