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In fairy tales of Aarne-Thompson folktale type 510B, the persecuted heroine, the heroine is persecuted by her father, and most usually, the persecution is an attempt to marry her, as in Allerleirauh or Donkeyskin. This was taken up into the legend of Saint Dymphna.
Several Child Ballads have the motif of incest between brothers and sisters who are raised apart. This is usually unwitting (as in the The Bonny Hind and Sheath and Knife, for example), but always brings about a tragic end.
There are also mentions of incest in the bible. In some cases, it can be logically inferred, since Adam and Eve (the supposed first people on earth) would have had to inbreed, since there were no other people.
Read more about this topic: Incest In Folklore