The Queen has said she is "delighted" at the birth of her eighth great-grandchild in an official notice.
Harry and Meghan's baby boy arrived this morning and has been described as "absolutely to die for" by his father.
This afternoon, hundreds of onlookers watched from outside of Buckingham Palace's gates as the bulletin announcing the birth was unveiled.
The framed message was placed in the forecourt of the palace for well-wishers to read.
Brought out just after 4.45pm from the Privy Purse Door, the announcement read: "The Queen and the Royal Family are delighted at the news that Her Royal Highness The Duchess of Sussex was safely delivered of a son at 0526am today.
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"Her Royal Highness and her child are both doing well."
Footmen Stephen Kelly and Sarah Thompson carried out the golden easel, followed by the bulletin in a wooden frame.
The palace's Union Jack flag was also taken down and replaced with a bigger one.
Waiting on the front gates was Jennifer Rice from Tennessee, who was travelling around Europe when she returned to London for the birth.
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The 48-year-old said: "I came back specifically for the baby announcement, I went to travel around Italy and France and came back last night when I knew it was getting very close.
"We've stayed up and watched all of the weddings, (Harry) just seems so real and I love Meghan.
"I think they might do a bit more American, maybe one of the names.
"I've never had the desire to come for the birth of the children but now I know it's part American it's part of us.
"I hope he's a redhead!"
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Alice Scammell, from Barnet, had been waiting outside the gates with her two children hoping to get a glimpse of the royal family.
The 26-year-old said: "Someone told us two hours ago that maybe a royal will turn up, we only came out on an outing but we thought we've got to get down.
"We're very excited."
Asked about names, she added: "I think they should call it Christopher, it's a very official royal name."
Travis and Lourdes Trainer arrived in London at 11am on Monday to celebrate their honeymoon.
The couple, from Miami, said they went straight to the palace after finding out the duchess had gone into labour.
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Mrs Trainer, 36, said: "I've always been a fan of the royal family, my mum was a fan of Princess Diana.
"It's always good news when someone has a baby and he seems so happy.
"It's a real interesting connection between the UK and US now, we've always joked that we're cousins."
Mr Trainer, 33, said he hoped the baby would be called James - his middle name - admitting: "I'm a little biased."
Meanwhile, despite it being a chilly Bank Holiday Monday, royal super fans have turned out in their droves to celebrate the arrival of a new monarch.
Union Jack bandannas, crusader costumes and makeshift town crier uniforms were all on display amongst the patriot gaggle that formed at the front of Windsor Castle.
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Earlier today, an official announcement said: "Her Royal Highness The Duchess of Sussex was safely delivered of a son at 0526hrs this morning.
"The baby weighs 7lbs 3oz.
"The Duke of Sussex was present for the birth.
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"The Queen, The Duke of Edinburgh, The Prince of Wales, The Duchess of Cornwall, The Duke and Duchess of Cambridge, Lady Jane Fellowes, Lady Sarah McCorquodale and Earl Spencer have been informed and are delighted with the news.
"The Duchess’s mother, Doria Ragland, who is overjoyed by the arrival of her first grandchild, is with Their Royal Highnesses at Frogmore Cottage .
"Her Royal Highness and the baby are both doing well."
