Prince William and Kate Middleton will celebrate their son Prince Louis' 5th birthday on Sunday. On Saturday, Prince and Princess of Wales shared new photos of their youngest son to mark the occasion. "Someone’s turning 5 tomorrow…A very happy birthday to Prince Louis," the couple wrote in the caption of their Instagram post, adding emojis of a birthday cake and partying smiley face. In the first image, Louis was seen smiling as he sits on top of a pile of leaves and grass in a wheelbarrow while being pushed by his mother, who beams at him.