The Frog Prince

 Once upon a time there were a king and his daughters.

 One day, the King's daughters went to the fountain in the dark forest. The youngest daughter was playing with a golden ball there. However she's golden ball fell into the water. Then a frog appeared and he said he can help if the princess become his friend and sleep with. the princess said 

she promise. The frog gave her the golden ball. But the princess broke her promise and left there.

 Next day, the frog visited the princess. He was going to sleep with the princess. The king made the princess to keep the promise. At night, the princess attacked the frog because she didn't want to sleep together. At the moment, surprisingly, the frog transformed into a prince. 

 Finally, the princess and the prince got engaged. The prince's servant came. He delighted to see the prince, who returned to human.

 

I think the princess is the lowest. I can't understand why the prince chose her.