His brother, Gwydion, wanted to help him rape Goewin. He accomplished this by stealing Pryderi of Dyfed's pigs, thus sending Math ap Mathonwy away to fight a war. Gwydion and Gilfaethwy were supposed to be with him, but they snuck back. Gwydion forced Goewin to stay with Gilfaethwy and he raped her. She told Math, and he turned them into animals. Gwydion was, for one year each, a stag, sow and wolf. Gilfaethwy was, for one year each, a hind, boar and she-wolf. Each year, they had a child together and Math turned the three children into people