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.
“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.
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!”
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.”