Prince William, Duchess Catherine, and their newborn son. Picture: Kensington Palace/Twitter

Catherine, Duchess of Cambridge, and her newborn son have left the hospital, hours after she gave birth.

The 36-year-old royal gave birth to her third child, and second son, with her husband Prince William on Monday morning, and seven hours after the tot was welcomed into the world, he and his mother are ready to head home from St. Mary's hospital in Paddington, London.

The news was confirmed by the Kensington Palace Twitter account, which shared a shot of Catherine - who already has four-year-old Prince George and two-year-old Princess Charlotte with William - alongside her 35-year-old husband, cradling their newborn baby in her arms.

A caption on the picture simply read: "Welcome to the family."

As of the time of writing, the new Prince is yet to have a publicly confirmed name.

Read: Brits bet on #RoyalBaby3's name

Shortly after the baby's birth, Kensington Palace confirmed in a statement: "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."

Both William and Catherine's 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."

Meanwhile, Prince William thanked the medical staff who helped deliver his son.

A separate statement read: "Her Royal Highness The Duchess of Cambridge will be leaving St. Mary's Hospital this evening. The Duke and Duchess of Cambridge and their son will travel home to Kensington Palace.

"Their Royal Highnesses would like to thank all staff at the hospital for the care and treatment they have received. They would also like to thank everyone for their warm wishes."