William III was the nominal Viscount of Narbonne

Viscount of Narbonne

The Viscount of Narbonne was the secular ruler of Narbonne in the Middle Ages. Narbonne had been the capital of the Visigoth province of Septimania, until the eighth century, after which it became the Carolingian Viscounty of Narbonne. Narbonne was nominally subject to the Carolingian Counts of...

 and Judge of Arborea (1407–1420).

He was the grandson of Beatrice, youngest daughter of Marianus IV of Arborea

Marianus IV of Arborea

Marianus IV , called the Great, was the Giudice of Arborea from 1347 to his death. He was, as his nickname indicates, the greatest sovereign of Arborea. He was a legislator and a warrior whose reign saw the commencement of massive codification of the laws of his realm and incessant warfare with the...

 and Timbra de Rocabertí, and Aimery VI of Narbonne (married 1363). When Marianus V

Marianus V of Arborea

Marianus V was the Judge of Arborea from 1387 until his death. His surname was Doria Cappai de Baux, the last part being a corruption of Bas-Serra...

, the youngest son of Beatrice' elder sister Eleanor

Eleanor of Arborea

Eleanor ; 1347 – 1404) was the giudicessa of Arborea from 1383 to her death. She was one of the last — and most powerful and significant — Sardinian judges; as well as the island's most renowned heroine....

, died in 1407, Arborea experienced a succession crisis. The late Beatrice had a claim to the judgeship which was picked up by her grandson, son of William II.

The real judge from 1407 was Leonardo Cubello, great nephew of Hugh II of Arborea

Hugh II of Arborea

Hugh II was Giudice of Arborea, reigning from 1321 CE until his death in 1336 CE. He was the illegitimate son of Marianus III of Arborea and Paulesa de Serra....

.