So one of the brothers Grimm stories is Allerleirauh. The Wikipedia article can sum it up pretty well but basically it ends with a king marrying his daughter. I'm thinking someone can easily do a follow up where the King weds beds and impregnates his daughter
Here's a summation of the story
https://en.wikipedia.org/wiki/Allerleirauh
and the story itself https://www.worldoftales.com/fairy_tales/Brothers_Grimm/Margaret_Hunt/Allerleirauh.html#gsc.tab=0
Here's a summation of the story
https://en.wikipedia.org/wiki/Allerleirauh
and the story itself https://www.worldoftales.com/fairy_tales/Brothers_Grimm/Margaret_Hunt/Allerleirauh.html#gsc.tab=0