With the Union flag raised, two footmen brought out a gold gilded easel on the forecourt of Buckingham Palace.
The formal notice, signed by doctors, reads: "Her Royal Highness The Duchess of Cambridge was safely delivered of a daughter at 8.34am today.
"Her Royal Highness and her child are both doing well."
Queues formed outside the Palace as royal well-wishers gathered to view the official birth announcement. The birth has also been announced on the BT Tower.
News of the new Royal Princess was announced this morning.
Kate was admitted to St Mary's hospital at 6am, and gave birth to her daughter just some two-and-a-half hours later at 8.34am.
The new princess weighs 8lbs 30z and Prince William was present at the birth. A name has yet to be announced, but Prince George now has a little sister!
News of the birth was announced on Twitter via Kensington Palace and by email.
A Royal Salute is to be fired in the Royal Parks and at the Tower of London on Monday (4 May) at 2pm to welcome the new royal baby.
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