Cheering crowds rushed towards the gates of Buckingham Palace as it was announced that the Duchess of Cambridge had produced a healthy male heir weighing 8lbs 6oz (3.8 kilos).
The as-yet unnamed baby is third in line to the throne and in the direct line of succession after Queen Elizabeth II’s eldest son and heir Prince Charles, and then his eldest son William.
“We could not be happier,” William, the son of Charles and the late Princess Diana, said in a brief statement.
US President Barack Obama and his wife Michelle led international tributes to the “joyous occasion” while Canada was the first to hail the birth among the 15 overseas realms to which the baby will be heir.
The former Kate Middleton, 31, spent ten hours in labour after she and William arrived around dawn at the private Lindo wing of London’s St Mary’s Hospital, Paddington, in central London.
“Her Royal Highness The Duchess of Cambridge was safely delivered of a son at 4:24 pm (1524 GMT),” Kensington Palace said in a statement just over four hours after she gave birth.
“The baby weighs 8lbs 6oz. The Duke of Cambridge was present for the birth.”
It was in the same hospital wing that the late Princess Diana gave birth to William in 1982.
Royal aides later placed a formal bulletin on a gold easel in the forecourt of Buckingham Palace which said that both Kate and her son were “doing well”.
Royal doctor Marcus Setchell added: “Wonderful baby. Beautiful baby”.
The queen, 87, said she was “delighted” while Prince Charles said he was overjoyed.