Queen Elizabeth Rules! Kate Middleton and Prince William's Daughter Will Be a Princess (If They Have One!)

Queen Elizabeth II officially states that daughters born to Charles' eldest son, the future Prince of Wales, will be Her Royal Highnesses, overturning a George V-era decree

Kate Middleton and Prince William's first child just may be a little princess. 

On what also happens to be the expectant mum's 31st birthday, Queen Elizabeth II decreed that her next great-grandchild's title will be prince or princess and be referred to as His or Her Royal Highness.

The legal decision—called a Letters Patent—overturns a 1917 decree issued by the queen's grandfather, King George V, that the Prince of Wales' eldest son would be prince but a firstborn daughter (or any daughter) wouldn't be a princess.

Quite the birthday gift for the Duchess of Cambridge!

A rep for the palace confirms to E! News that the Letters Patent states: "All the children of the eldest son of the Prince of Wales should enjoy the style, title and attribute of Royal Highness with the titular dignity of Prince or Princess prefixed to their Christian names."

As if the London Olympics Opening Ceremony weren't enough proof, here's another instance of how the queen is positively rockin' it at 86.

Additionally, the Succession to the Crown Bill, determining that the Duke and Duchess of Cambridge's first child will be a monarch, regardless of its sex (which we still don't really know, sigh), was just published last month. Once the House of Commons presumably votes it into law when parliament resumes, it will end the centuries-old tradition of male heirs being first in line for the throne, regardless of their birth order.

The bill also "allows" those in line for the throne to marry Roman Catholics.

Not a bad addition to the legacy of the reigning monarch, right? Diamond Jubilee, indeed.