Mary, Crown Princess of Denmark, has changed royal fashion forever. The princess has paired a a white tweed dress with runners. Who knew athleisure would catch on so much?

Princess Mary paired the dainty dress by Danish designer Mark Kenly Domino Tan with Nike runners. The estimated price for the ensemble is $280, an affordable price for paupers and princesses alike.

Let's not get too carried away as the princess has kept to many of the royals' infamous fashion rules. For one, her dress follows protocol perfectly.

The rules state upon wearing a dress, tan tights are a must. Hemlines and necklines should be appropriate at all times. Strictly no cleavage and dresses must be at such a length that no one can see the hiney of the highness.

Royals must wear bright colours to be seen in a crowd, mainly for security reasons. They are never to wear black unless mourning, however a black outfit is required on every trip in the case of a sudden death. Queen Elizabeth refuses to wear beige as she believes people will not be able to spot her on an outing. Princess Mary's white midi dress is a perfect fit for the royal rules.

However when it comes to footwear there aren't many rules in place. Wedges are not to be worn around Queen Elizabeth and no open toe shoes are allowed at all. Some celebrity guests rebelled against this rule at the Duke and Duchess of Sussex's wedding. Long time friends of Meghan Markle, Priyanka Chopra and Troian Bellisario wore open toe heels to the royal wedding.

Shoes have to be clean and tidy. It has been rumoured that Prince Charles even has his shoelaces ironed as part of this strict rule. If Mary, Crown Princess of Denmark, has the laces of her Nike runners ironed then she's following the rules accordingly.