Gregorius or The Good Sinner is a Middle High German narrative poem by Hartmann von Aue. Written around 1190 in rhyming couplets, it tells the story of a child born of the incestuous union of a brother and sister, who is brought up in a monastery, ignorant of his origins, marries his mother, repents of his sins and becomes pope. Plot. Gregorius' parents are aged approximately 11 when he is born and are the orphaned children of a wealthy duke, and his father dies after being sent on a pilgrimage from Europe to Jerusalem to repent of their sins by a wise old man.
https://en.wikipedia.org/wiki/Gregorius