There is a story in the Mabonogion called “Math the Son Of Mathonwy” that tells of Gwydion and Gilfaethwy, who raped Goewin, the daughter of Pebin. Gwydion and Gilfaethwy were the maternal nephews of Math ab Mathonwy, who was lord over Gwynedd. Goewin was under the protection of Math, and Gilfaethwy had become greatly enamored of her.
The two concocted an adventure to acquire swine, which were unheard of in that time, from Pryderi, king of Dyfed. Gwydion, being a magician (trained by Math in those arts), conjured illusions to trick Pryderi into trading him the swine for apparitions of fine horses and greyhounds. The trick would only last a day and the brothers and their retinue quickly fled back to Gwynedd. They reached Caer Dathyl, Math’s residence.
That night, after Math and his men had left to secure the swine, Gilvaethwy stayed in Math’s chambers, and he and Gwydion rudely chased out all of the women from the chamber, except for Goewin, who they forced to remain.
On the next day a battle ensued between Math’s and Pryderi’s men over the trickery of Gwydion. Pryderi suffered major losses and negotiated terms of peace. Pryderi made his case against Gwydion, whom he called out for battle. With Gwydion’s magical advantage, he slew Pryderi.
After Math and his men returned home triumphant, he went back to his couch and placed his feet on Goewin’s lap, as was tradition at that time for a lord with his maiden. She informed him she could no longer fill that role, as she had been defiled. She told Math how Gwydion and Gilfaethwy had raped her. Math declared to avenger her honor and took her as his wife, bestowing upon her dominion of his lands.
Gwydion and Gilfaethwy avoided Court in a form of self exile, until it was forbidden for others to provision them. After a while, they returned to Math’s Court. They made kind speech to the kings, but he was set on punishing them for the needless deaths of many of his warriors, with the death of Pryderi being the only worthy action they had done. He then commenced to inflict punishment upon them.
Being a very strong magician himself, Math took out his wand and turned the two into deer. He commanded them to mate and return to him in a year. After the year, they returned, with a fawn. He then struck them with Magic to turn them into wild hogs. He took the fawn and turned him human, having him baptized and naming him Hyddwn, meaning “Stag-man”.
A year later the brothers in the form of wild hogs returned to him with a young hog with them. He then turned the brothers into a pair of wolves. He took the young hog, turned him human, had him baptized, and named him Hychddwn Hir, or “”Sow-man the Long”, for the long auburn hair that he had.
After the third year, the brothers returned with a wolf cub. He took the cub, turned him human, had him baptized, and named him Bleiddwn, or “Wolf-man”. He then told the brothers that his punishment of them was complete and turned them back into humans. They were washed and restored to their noble state.
So take it for what it’s worth. Let not facts get in the way of romantic legends.