Watch: The moment Kate and William reveal their new baby boy to the world outside London's exclusive St Mary's Hospital

Kate Middleton has given birth to a healthy baby boy in the Lindo wing of London's exclusive St Mary's Hospital today with Prince William by her side.

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The baby was delivered about 10pm last night, New Zealand time.

Royal officials say the baby weighed in at eight pounds, seven ounces (3.8 kilograms).

Her Royal Highness and child are both reportedly doing well.

The new arrival is the Duchess of Cambridge and Prince William's third baby, joining brother George aged four and sister Charlotte aged two.

The royal couple have not announced the baby's name yet but people are placing bets on what it could be.

1 NEWS' Europe Correspondent Joy Reid says the most popular names are Albert and Arthur.

The news comes amidst a busy couple of months for the royal family with Prince Harry and Meghan Markle to be wed on May 20.

A few hours after the birth the Duchess of Cambridge and Prince William hospital and are headed home with their newborn son.

The duchess, emerged from St. Mary's Hospital about seven hours later alongside her husband, holding the baby wrapped in a white blanket.

The trio posed for photographers before going back inside.

The royals emerged a few minutes later with their infant in a carrier and got into a waiting car.

The newborn prince's elder siblings, Prince George and Princess Charlotte, already had gone home after a brief first meeting with their baby brother.

The prince, whose name has not been released, is fifth in line to the British throne.