As Kate - wearing a red Jenny Packham dress - held the new arrival William said "we're very happy'
They went back inside and reemerged with William holding the baby in a carry cot.
After putting him in the back of the Range Rover he said "Very happy but we've now got thrice the worry! At least we didn't keep you waiting.'
The happy couple then drove off to Kensington Palace to start life as the "Famous Five"
Earlier, a beaming and clearly proud Prince William drove off and returned half an hour later with his two children George and Charlotte to see their new brother for the first time. A thrilling day for royal fans everywhere!