In "Letters Patent Under the Great Seal of the Realm" dated Dec. 31, the queen said her great-grandchildren will have "the titular dignity of Prince or Princess prefixed to their Christian names," The Daily Telegraph reported. They will be entitled to be formally addressed as "your Royal Highness."
The queen's decree was published Wednesday in the Royal Gazette. Under a 1917 decree by her grandfather, George V, only the oldest son of the prince of Wales is automatically entitled to the rank of prince at birth.
The royal succession is currently in a state of flux with Britain and the Commonwealth countries that have the British monarch as head of state agreeing to make the process gender neutral. If the duchess's first child is a daughter, she has a good chance of becoming queen.
Wednesday was also the duchess's 31st birthday. Prince William, taking a day off from his Sea Rescue duties in Wales, celebrated with her in London, the Telegraph said.