In the First Continuation of Chrétien’s Perceval, a half-man, half-boar who was the product of a union between the sorcerer Eliavres and a sow. King Caradoc of Nantes had discovered that Eliavres was having an affair with Caradoc’s wife, and he forced Eliavres to copulate with the pig as punishment.
There is probably a connection to Twrch Trwyth of Welsh legend.
Source
First Continuation of Chrétien’s Perceval | Attributed to Wauchier of Denain, c. 1200