Frisons
The King of Dessemoume in Ireland in the French Les Merveilles de Rigomer.
Lancelot rescued Frion’s daughter, Martha, from a pack of kidnappers, for which Frion offered Lancelot the girl and the kingdom. When Lancelot refused, Frion attempted to trick him into remaining in Dessemoume, but Lancelot recognized the ruse and departed.
Frion later helped Arthur’s men conquer Rigomer Castle.
See also
Desmond | The Legend of King Arthur
Source
Les Merveilles de Rigomer | Jehan, mid to late 13th century