To the delight of crowds of reporters, cameramen, photographers and well-wishers, the royal aide left the hospital via the main entrance to make the two-mile journey to Buckingham Palace where the bulletin was displayed.
The brief bulletin, presented on palace-headed foolscap-sized paper, confirmed the baby was a boy, weighed 8lb 6oz and came into the world at 4:24pm.
A waiting driver, accompanied by a police escort, took the notice through the streets of central London to the Privy Purse door at the front of the palace.
The bulletin, signed by the doctors after the birth, was placed on the ornate easel behind the gates.
A last-minute change of plan from the Palace revealed that the first news of the baby's arrival would break via a press release rather than the easel method as was first suggested.
The town crier also made an announcement in traditional dress to the huge cheers and applause of the gathered crowds outside the Palace.
The Queen, Prince Charles, Prince Harry and Kate's parents Carole and Michael Middleton had already been informed of the birth, which took place on Monday afternoon.
Prince Charles released a statement saying that he was "overjoyed" at the birth of the future heir and that becoming a grandfather for the first time was a "unique moment".
The Duchess will remain in hospital overnight. She and the baby, who weighed 8lb 6oz, are said to be doing well.