It's only been open a matter of hours but the Shard observation deck has already been commandeered by hopeless romantics.
James Episcopou, 22, was rewarded for his bravery when his girlfriend Laura Taylor, also 22, said yes.
Although it may be the first proposal, it is far from the first "romantic action" the Shard has entertained.
Last month the Sun reported how women's knickers had been found in the men's toilets on the viewing platform.
The mayor of London cut a ribbon just over 800ft (244m) above the capital to welcome visitors to the highest vantage point in western Europe.
He was joined on level 72 of London's tallest building by its architect, Renzo Piano, for the opening of the attraction, The View from The Shard.
Piano said: "This building is magic for a number of reasons.
"First, because it's in London, second, because it's so tall, and third, because this building is a part of London. It's a sense of London.
"It's sad when London is sad, it's joyful when London is brilliant and joyful."
Johnson described the building as "a most amazing place".
He said: "I don't think there's anything in London like this.
"It's the closest thing to being in an airplane and looking down on London. But you can walk around, you've got complete stability.
"You can see all the bends in the river, you can see my office, you can see Buckingham Palace, you can see the whole thing for 40 miles around."
On a clear day, visitors to the Shard, which towers over the city at a height of 1,016ft, are promised a spectacular view of the capital.
But visibility was restricted for the dignitaries, journalists and members of the public attending the launch because of wet and cloudy weather.
Some 4,800 people have paid for admission on Friday - at £24.95 for adults and £18.95 for children.
On a clear day, visitors will be able to enjoy a 360-degree view of the capital's skyline, from a platform almost twice the height of any other in the city.
With the help of specially-designed telescopes, they should be able to pick out London's landmarks in the streets below.
Visitors to the attraction - on floors 68, 69 and 72 - are whisked up in two high-speed lifts in around 60 seconds.
Irvine Sellar, chairman of Sellar Property and developer of the Shard, said: "I think Londoners will feel ownership of the Shard.
They'll adopt it as the Parisians adopted the Eiffel Tower or the Americans adopted the Empire State.
"I think we need a new landmark building, something that stands out."
Anders Nyberg, chief executive of The View from The Shard, claimed it offered a unique experience.
"You're seeing a tapestry of history," he said.
"We're in a 21st Century tower, right across the river from an 11th Century tower, the Tower of London.
"Nowhere else in the world can you get that kind of perspective."