The newest member of the royal family arrived this morning after the Duchess of Cambridge gave birth to a girl, Kensington Palace said today.
The baby girl was "safely delivered" at 08:34am this morning and weighed 8 lbs 3 oz.
"Her Royal Highness and her child are both doing well," the palace said in a statement.
The child will be fourth in line for the throne, behind grandfather Prince Charles, father Prince William and brother Prince George.
The couple are yet to announce a name for the new born, although bookies have suggested Alice or Charlotte.
The duchess was admitted to the Lindo Wing at St Mary's Hospital in west London in the early hours of this morning, which is the same hospital where their son Prince George was born just under two years ago.
She had been taken to the hospital by car and was accompanied by Prince William.
Officials had previously said that the couple do not know the sex of their unborn child.
William was born in a private wing at the same hospital on June 21, 1982. So was his son, George.
His father Prince Charles was born at Buckingham Palace.