On Tuesday, Princess Charlotte Elizabeth Diana. William signed the registry at Kensington Palace overseen by a registrar from Westminster Register Office.
The Duke filed the official document on the same day Princess Charlotte met her great-grandmother the Queen for the first time. William and Kate Middleton, introduced their newborn baby to Her Majesty in their apartment at Kensington Palace.
Royal fans were quick to note that under the "occupation" heading for Kate, William wrote, "Princess of the United Kingdom," while their address was signed as Kensington Palace.
Princess Charlotte is the first girl to have been born to a direct heir to the throne since the Queen gave birth to Princess Anne 64 years ago, and is the monarch's fifth great-grandchild.
Other members of the royal family to have already met the new Princess include an "absolutely delighted" Camilla. Kate's parents Carole and Michael Middleton also visited the family at Kensington Palace along with their daughter Pippa on Sunday.
Meanwhile Prince Harry has said that he "can't wait" to meet his "absolutely beautiful" niece when he returns from Australia.
The nation had been eagerly waiting to hear what William and Kate would name their baby girl after her arrival on May 2. "Her Royal Highness The Duchess of Cambridge was safely delivered of a daughter at 8:34am," Kensington Palace announced on Twitter. "The baby weighs 8lbs 3oz. The Duke of Cambridge was present for the birth. The Queen, The Duke of Edinburgh, The Prince of Wales & The Duchess of Cornwall, Prince Harry & members of both families have been informed. Her Royal Highness and her child are both doing well."