"Princesses exist" is not a trope on their own. You may be looking for one of the following:

* GoodPrincessEvilQueen -- the (usually) younger and more beautiful princess is morally superior to the older and often less attractive Queen.
* GratuitousPrincess -- princesses exist in a setting or culture that doesn't actually have royalty, or when there are more princesses than plausible in the setting (e.g. having an entire school of princesses).
* HonoraryPrincess -- the character is not a princess, but is referred to as such to show off her distinguished status.
* PrincessProtagonist -- the lead character is a princess, because what little girl wouldn't want to imagine herself as one?
* RagsToRoyalty -- an everygirl is given the title of princess or is {{re|allyRoyaltyReveal}}vealed to be the missing heir to a throne.
* SaveThePrincess -- the DamselInDistress is a princess because rescuing a kidnapped princess (and possibly [[StandardHeroReward winning her hand in marriage]] as a result) is so much more glamorous than saving Plain Jane.

For tropes about princesses in general, see PrincessTropes.

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