In Wirnt von Grafenberg’s Wigalois, an country in Africa ruled by Prince Lion. Gawain’s son Wigalois took control of the land when he defeated Lion in a war.
The Belgian province may be the source of the name, but Wirnt specifically places it in Heathendom.
Source
Belgium | The Legend of King Arthur
Source
Wigalois | Wirnt von Grafenberg, early 13th century