The birth of a baby is always cause for rejoicing, but the arrival of a prince who will be king is a moment in history.
The event was announced with a 62-gun salute and wild jubilation, not just in the Commonwealth, but around the world.
There are monarchies in the world today that are older, richer and more powerful than Great Britain's, but no other royal birth or event causes such a stir. It was almost as if he was the only baby born in the world.
Even the Americans, who revolted against the Queen's distant grandfather, George III, retain a special fondness for the British royal family.
The birth of a healthy son to the Duke and Duchess of Cambridge (William and Kate) represents the continuation of a 1,000-year tradition that may be filled with blood and guts, but also with justice, the growth of democracy and the rule of law.
The royal couple's son is a living link with that past and its ancient traditions and customs.
His parents may be no prouder than any other father and mother with great hopes for their offspring, but the difference is that this week a king was born.
The energetic response to his birth, and to the marriage of his parents two years earlier, is evidence the historic institution remains relevant to millions of people, particularly in the Commonwealth. At times such as these, it provides an iconic moment in which a people can at once revere and rejoice in those things that we share in common.
May he live long and glorious.