Two American girls debate what Kate Middleton will look like at her wedding in five days' time even as the famed Changing of the Guards ceremony takes place behind them at Buckingham Palace.
"I am excited about the dress. She will have something big", predicts Amanda Hijazin, 13, wearing a lacy top and with braces on her teeth.
"No, something simple, graceful, elegant, fabulous", her friend replies.
"I am not going to be here, but to know that they will be there, it is very nice", she adds.
"The girls are fanatical about the prince!", says Rebecca Adams, a teacher of English who is looking after the young Californians on their visit to the British capital.
"They are also interested in the younger prince", she laughs, referring to William's younger brother Harry, who will be best man at the wedding.
The teenagers wanted to stay for the wedding but it was impossible to change their tickets as the planes were full, Adams says.
"We will watch the wedding on TV. It will start at 2am (Los Angeles time) -- I will set my alarm!", says Amanda.
Adams remembers watching the wedding of William's parents, Prince Charles and Princess Diana, on television in 1981 when she herself was at high school.
"A generation later, they will do the same thing," she says about her students.
Crowds of hundreds of people around 50 deep were gathered to watch the ceremony in bright sunshine, far more than usual.
The hotly-awaited royal wedding is expected to more than double the number of visitors to London with an extra 600,000 tourists from home and abroad expected to flock to London for the service.
Tourists were also out in force outside Westminster Abbey where the royal couple will tie the knot on Friday but they were not allowed inside because services were underway for Easter.
"We wanted to see the church where they're going to get married but it's shut!" says Silvia Bosisio, an Italian woman who like many others had taken advantage of the long weekend to visit London.
"They're a nice couple, it's a shame we can't stay for the wedding," says the young blonde, who works in a wedding agency.
But there are no such problems for the Slade family from San Francisco, in the United States.
"We booked this trip to London in October so it is such a happy coincidence that it's the same time as the wedding," says Randy Slade, who is here with his wife and granddaughter.
"We'll be watching. I think it will be an overwhelming occasion. We are huge fans of the royal family. I think the queen is lovely, she is such a consistent presence in changing times."
His granddaughter Megan, an 18-year-old student, adds: "Kate is awfully pretty. I just want to see her dress!."
Koshi Kawata, a Japanese boy aged nine, said he too was "so happy."
"I am going to tell my friends that I saw where they will get married", he says as his mother looks on with a smile.
However, the Gache family from Saint Etienne in southeastern France are disappointed to be in London for the run-up to the wedding.
"It's rammed. There are so many people," said Fabienne Gache, the mother.
"We'll watch the wedding on television to see what the palace looks like -- because today you can't see anything!" joked her son Clovis, aged eight, as he tried to see past the crowd.