The arrival of William and Catherine's third child will be marked with a traditional bulletin on show at Buckingham Palace.
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Just as when Prince George and Princess Charlotte were born, the new royal baby's birth will be celebrated with the age-old custom of placing a paper proclamation for the public to see at the Queen's London residence.
A brief formal announcement - on foolscap-sized paper set in a dark wooden frame - will be placed on an ornate golden easel on the forecourt of the Palace.
It confirms the sex of the baby and the time of birth, but gives little else away, other than usually revealing that the baby has been "safely delivered" and mother and child are "doing well".
It used to be hand-written, but is now typed.
It will also be signed at the hospital by the doctors who tended to the duchess, and then ferried back to the Palace by car.
Just like with George and Charlotte, an initial official announcement will be emailed to the press by Kensington Palace, coinciding with a confirmation of the birth via Twitter.
News of a new prince or princess is unlikely to be announced overnight as the Queen and members of both families will have to be informed first.
The names given to royal babies are not usually revealed straight away, and the public is often left guessing for several days.
William and Kate took two days to announce both George and Charlotte's names, informing the Queen of their choice beforehand.
The birth will be celebrated with a 41-gun salute in Green Park or Hyde Park - and a 62-gun salute at the Tower of London.
Australian Associated Press