Germans, Australians and Americans were among those flocking to Buckingham Palace to cheer the new baby boy's arrival.
Royalists screamed with excitement as the happy news spread to those waiting outside the palace.
One man shouted: "It's a boy," prompting crowds to erupt into spontaneous cheering, ahead of the easel being placed in the forecourt.
Three were three cheers of "hip hip hooray," as the crowd outside the palace gates swelled to more than 10 deep.
Many had been waiting patiently for confirmation of the birth ever since news of the Duchess going into labour this morning.
The months of speculation and anticipation - dubbed the Great Kate Wait - built to a climax this morning amid news that the Duchess of Cambridge had been admitted to hospital in the early stages of labour.
The new arrival was announced in traditional style
Matthew and Donna Harold, from Michigan in the United States, said they had been asked to stock up on commemorative souvenirs for friends back home during their holiday in London.
"The royal baby is front-page news every day back in the States at the moment, there is a lot of excitement," said Mrs Harold.
"Our holiday was booked months ago, so we did not expect to be over here while the baby was happening, so we have been told to bring back as many newspapers and souvenirs with the baby on as possible."
In Australia, a set of commemorative baby stamps has already been commissioned to mark the royal birth.
Lynette Traynor, a postal worker from Melbourne who is on holiday in London, said: "We love everything to do with the royals, so the news is full of it.
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"We have a set of baby stamps ready to go, as soon as it has been confirmed. We can't get enough of it."
Another visitor to the Palace, 26-year-old German Veronika Schwarz, said she thought there was greater excitement outside of England.
"We don't have anything like the Royal Family in Germany, so we are all getting quite carried away with this."
A handful of royal fans have spent days camped outside the Lindo Wing of St Mary's hospital, eager to snatch a glimpse of the baby and future sovereign.
Glaswegian couple Douglas Johnstone and Victoria Wallace said they felt fortunate that their trip to London coincided with the royal birth.
Mr Johnstone said: "We are very lucky to have planned our trip at this time."
Police chatted with visitors, many pondering potential names for the newborn future monarch.