The Dukedom of Aveiro was an aristocraticPortuguesetitle, granted in 1535 by King John III of Portugal to his 4th cousin, John of Lencastre, son of InfanteGeorge of Lencastre, a natural son of King John II of Portugal. John of Lencastre was already Marquis of Torres Novas when the King granted him the new title of Duke of Aveiro. Later, their descendants strongly supported Philip II of Spain during the 1580 Portuguese succession crisis. Thus the Dukes became the second aristocratic House ofPortugal, after the Braganzas. Raimundo of Lencastre, 4th Duke of Aveiro maintained his House's traditional support for the Habsburg monarchy, even after the 1640 national revolution in Portugal. Therefore the Aveiro property was confiscated by the new Kings of the Braganza Dynasty, and granted in 1668 to his uncle, Peter of Lencastre, who already was Archbishop of Évora and general Inquisitor, becoming 5th Duke of Aveiro. He died in 1673 without issue. The succession was given to his niece, Maria de Guadalupe of Lencastre, who was married to the Spanish Duke of Los Arcos. She returned to Portugal with her younger son, while her husband and her older son stayed in Spain. She regained the control of her House and estates and recognised the Braganzas royalty. Due to the participation of the 8th Duke of Aveiro in the Távora affair, all the possessions of the Dukes of Aveiro were confiscated, their coat-of-arms destroyed from the public places, their houses demolished and their lands salted. Only the Palace of the Dukes of Aveiro in Azeitão, Portugal remains as a testament to the family's previous might and power. . The Aveiro palace in Lisbon, demolished and salted, gave place to a stone memorial in order to perpetuate the memory of the shame of the Aveiro House. In it the following text can be read : Aqui foram arrasadas e salgadas as casas de José Mascarenhas, exautorado das honras de Duque de Aveiro e outras condemnado por sentença proferida na Suprema Juncta de Inconfidencia em 12 de Janeiro de 1759. Justiçado como um dos chefes do barbaro e execrando desacato que na noite de 3 de Septembro de 1758 se havia commetido contra a real e sagrada pessoa de D.José I. Neste terreno infame se não poderá edificar em tempo algum. After 1759 the title was extinct. However, in 1939, Duarte Nuno, Duke of Braganza, authorized the use of the personal title of Duke of Aveiro to Caetano Henriques Pereira Faria Saldanha de Lancastre, Count of Alcáçovas, who did not use the prerogative. The only legitimate relatives of José de Mascarenhas da Silva e Lencastre, 8th Duke of Aveiro, are descended from his sister Francisca das Chagas Mascarenhas and her husband the 1st Marquis of Lavradio.
José de Mascarenhas da Silva e Lencastre, 8th Duke of Aveiro, collateral line, descending from Álvaro and Juliana of Lencastre through female line. He was executed by the Marquis of Pombal under orders of King Joseph I of Portugal, due to his participation in the Távora affair, a conspiracy against the king.
When Peter of Lencastre, 5th Duke of Aveiro died in 1673, his niece Maria de Guadalupe of Lencastre was finally recognised by the Portuguese King as Duchess of Aveiro in 1679, on condition that she return to Portugal although she was married to the Spanish Duke of Los Arcos. Her husband opposed this; she divorced him, returned to her homeland and regained the House of Aveiro and their estates. While the divorce was pending, King Carlos II of Spain tried to prevent her return to Portugal by granting her, in 1681, the Spanish title of Duchess of Aveyro. This title belongs today to the Spanish Carvajal family, with no relationship to the Lancastre family of Portugal. It is not a Portuguese title and is entirely separate from its Portuguese homonym.
