Willem, for unknown reasons, killed Yoren's older brother and fled town that night. From then on, Yoren started to become obsessed with him, thinking about him whenever he did anything, going as far as to whisper his name before going to bed. Willem returned to his hometown years later and Yoren says he "put an axe so deep into his head, they had to bury him with it", getting revenge of him. Knowing he'd be executed, he fled to The Wall to try and live as free as possible.
In the booksEdit
In the A Song of Ice and Fire novels there are several characters whose first name is Willem (Willem Darry, Willem Frey, Willem Lannister), but none of them has anything to do with Yoren or his family. Yoren never speaks of his relatives.