Middleton's new title was officially used for the first time on Friday, as Prince William, 31, registered their son by signing the birth register at Kensington Palace this morning.
According to a photo of the registry, William's occupation was listed as "Prince of the United Kingdom" while Middleton's was referred to as "Princess of the United Kingdom."
The Duchess of Cambridge may have a job as a princess, but by name she is still just a duchess. Her name was listed as, "Catherine Elizabeth Her Royal Higness The Duchess of Cambridge" while her husband's name included the title "Prince."
The new mom, 31, and baby George are currently staying with her family about 50 miles away from London in Bucklebury.