The Duke and Duchess of Cambridge have called their new baby Louis Arthur Charles.
William and Kate's third child - who is fifth in line to the throne - was born on Monday.
He weighed 8 pounds 7 ounces.
The Duke and Duchess of Cambridge are delighted to announce that they have named their son Louis Arthur Charles.— Kensington Palace (@KensingtonRoyal)
The baby will be known as His Royal Highness Prince Louis of Cambridge.
He's a little brother for Prince George and Princess Charlotte.