The old fairy tale about the Prince who was a frog until a princess was actually a Brother's grim fairy tale. I will just give an outline if you are unfamiliar.
Girl drops ball in water well. Promises a talking frog anything if he will get the ball. When she talks to the frog her exact words were--"Whatever you will have dear frog, my pearls and jewels and even the Golden crown I am wearing."
Frog returns to her the ball and disappears without taking the frog with her. She had not kept her promise. He knocks on her door at home while the King is eating with all of his couriers.
He hears her story and replies to her-"That which you have promised you must perform."
She begins crying but lets the frog eat off of her plate. After he announces "I have eaten and am satisfied; now I am tired. Carry me to your little room and make your silken bed ready, we will both lie down and go to sleep.
I was thinking of having her around 17 dropping something more valuable then a ball and having some kind of monster play the role of the frog.
Only now after many woman have not kept there promise, and even this one had to be forced into keeping her word he wants revenge.
There can be an eventual love affair but perhaps that takes time.
He does turn into a handsome prince after their first Kiss, but one with a bit of an attutude. Perhaps some magic if we want to retell it that instead of having been turned into a frog perhaps it was a result of using magic incorrectly.