Caradoc of Nantes and Vannes
The King of Nantes and Vannes and husband of Ysave, niece of Arthur.
His wife engaged in an adulterous affair with a sorcerer named Elïavrés, and gave birth to a son, accepted by Caradoc as his legitimate heir and also named Caradoc (Briefbas). To hide the affair, Elïavrés used magic to make Caradoc believe he was making love to his wife when, in fact, he was copulating with various animals.
When the younger Caradoc, having become one of Arthur’s knights, exposed the affair, King Caradoc imprisoned his wife and forced Elïavrés into bestiality with the same animals with which Caradoc had been tricked into sleeping.
Source
First Continuation of Chrétien’s Perceval | Attributed to Wauchier of Denain, c. 1200