The title duke of Terceira, de juro e herdade (meaning "forever granted") was created by decree of King Pedro IV of Portugal, on 8 November 1832.

Heads of the Portuguese branch of that family have been ennobled since the marriage of Constance Manoel with King Pedro I of Portugal.

Her brother, Henrique Manoel, was brought into her entourage, and he was made Count of Seia, in Portugal, by his brother-in-law, the king.

The family dates back to the first count of Vila Flor D. Sancho Manoel de Vilhena, descent in male line from Juan Manuel de Villena, the second son of the 3rd Lord of Cheles, knight of the Order of the Golden Fleece and Mayordomo-Mor of the Emperor Charles V, who descended from the Infante Juan Manuel, Prince of Villena, the grandson of King Fernando III of Castile.

He won the Battle of Asseiceira, which put an end to the civil war, and he signed the peace treaty (Concession of Evoramonte) on behalf of King Pedro IV of Portugal.