The Emperor of Saxony when Tristan served as the King of Spain. Donísus asked for Tristan’s help in combating a king named Amilías, who was making frequent raids in Donísus’s country. Tristan killed Amilías, and Donísus rewarded him with many lands and treasures.
Later, Tristan’s son, Kalegras, married Lilja, Donísus’s daughter.
Source
Saga af Tristram ok Isodd | 14th century