Prince William has left St Mary's Hospital in London following the birth of his third child.

The 35-year-old royal was present when his wife Duchess Catherine gave birth to their as-yet unnamed son at 11:01am, and the Duke of Cambridge has now departed the hospital to see their older children, Prince George, four, and Princess Charlotte, two, at their Kensington Palace home.

William - who arrived at the hospital with his wife shortly before 6:00am on Monday (23.04.18) - waved to the crowds gathered outside the hospital before getting in his car and heading to Kensington Palace.

Although the prince didn't make a statement, he promised the crowd that he'd be ''back in a minute'' before getting into his vehicle.

News of the birth was first announced by Kensington Palace, who revealed that the young prince weighed 8lbs 7oz, at 1:03pm.

In a statement, the royal house shared: ''Her Royal Highness The Duchess of Cambridge was safely delivered of a son at 1101hrs.

''The baby weighs 8lbs 7oz.

''The Duke of Cambridge was present for the birth.

''Her Royal Highness and her child are both doing well.''

The statement added that the Duke and Duchess' families are ''delighted'' with the new addition to the household.

The statement concluded: ''The Queen, The Duke of Edinburgh, The Prince of Wales, The Duchess of Cornwall, Prince Harry and members of both families have been informed and are delighted with the news.''

Earlier in the day, Kensington Palace announced that Catherine - who was known as Kate Middleton prior to her marriage in 2011 - had been admitted to hospital after going into labour.

A statement read: ''Her Royal Highness The Duchess of Cambridge was admitted to St. Mary's Hospital, Paddington, London earlier this morning in the early stages of labour.

''The Duchess travelled by car from Kensington Palace to the Lindo Wing at St. Mary's Hospital with The Duke of Cambridge.''