A sea of union flags, banners and costumes filled the street outside the Lindo Wing, awaiting the news of William and Kate's baby boy.
There were loud cheers as the self-proclaimed Royalist Town Crier emerged to announce the birth of George and Charlotte's little brother – born at 11.01am weighing 8lb 7oz.
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Many had been camped outside the hospital for days – some even weeks – having been present for the birth of the baby's older siblings George and Charlotte.
On the news that the Duchess of Cambridge had given birth to a boy, the sound of applause and champagne corks popping filled the air.
Among the crowd were Mandy and her partner John, who had travelled from Somerset for an appointment and were pleasantly surprised to realise their trip coincided with the special occasion.
Mandy joked: "We were really surprised by our huge welcoming committee. Totally unexpected.
"We heard on the news that there's a Royal baby on the way. Luckily we did make our appointment."
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Perhaps the most popular man among the crowd was John. He had been outside the hospital for 15 days.
He spent the wait before the announcement entertaining the crowds with his singing.
He said: "I'm very excited. I was told at 8am this morning she was in the Lindo Wing. What a day. And it's St George's Day. We're going to celebrate with some fish and chips, and an England flag. And we'll be singing 'Congratulations'."
John popped open a bottle of champagne upon hearing the news that a new prince had been born.
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Julie, on holiday from Australia, happened to be staying in a hotel nearby and decided to cancel a trip to Windsor Castle to join the crowds when she heard the news.
She rightly predicted the sex of the baby.
She told Sky News before the news broke: "I got to take a picture with a police officer right outside the hospital in that iconic spot.
"We walked past here last night and there was nobody around. I think she'll have a boy. Our family back home also thinks it will be a boy. We were meant to visit Windsor Castle today but I think we'll stay here and wait."
Bookmakers say the most popular choices for names are Arthur, James, Philip and Albert.
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