Tristan’s wife in the Icelandic Saga af Tristan ok Ísodd, essentially the same character as Isolde of the White Hands.
The sister of Earls Siguròr and Hríngr of Spain, she was offered to Tristan when he conquered the kingdom. They had a son named Kanelgras (Kalegras) who eventually became king of England. Like Isolde of the White Hands in the traditional legend, Isolde the Dark was jealous of Tristan’s love for her namesake in England.
Tristan was eventually wounded in combat, and he sent to England for the other Isolde (an experienced healer), telling the shipmaster to fly white sails during the return voyage if she was on board, and black sails if she was not. Isolde the Dark, seeing the ship returning with white sails, lied to Tristan and said they were black. Tristan died immediately from sorrow.
Note
Variant of Iseult used in the thirteenth century by Gottfried von Strassburg, and in the nineteenth century by Richard Wagner.
Sources
Saga af Tristram ok Isodd | 14th century
”Tristrams Kvædi” | Early 15th century