John of Lencastre, 1st Duke of Aveiro

João de Lencastre ( ?, 1501 – Coimbra, 1571), was the older son of Infante George, Duke of Coimbra and of his wife Dona Beatriz of Vilhena.

Through his father, John was a grandchild of King John II of Portugal and a 3rd cousin to King Manuel I of Portugal.

Through his mother, daughter of Álvaro of Braganza (4th male son of Fernando I, 2nd Duke of Braganza), John of Lencastre was close related to the most prestigious families of the Kingdom (namely the Duke of Braganza, the Marquis of Ferreira, the Marquis of Vila Real, the Count of Vimioso, the Count of Portalegre).

When he was 12 years old, he served crown prince John (who became later King John III of Portugal) and King Manuel I granted him the title of Marquis of Torres Novas by a royal decree issued on March 27, 1520.

In that time, the royal house announced the marriage of Infante Ferdinand, Duke of Guarda (King Manuel I younger son) to the richest and prestigious heir Dona Guiomar Coutinho, 5th Countess of Marialva and the 3rd Countess of Loulé. However, John of Lencastre declared he had secretly married the richest bride. The scandal in the Court ended when King John III ordered the Marquis imprisonment in the Castle of São Jorge, in Lisbon, allowing the celebration of the Infante Ferdinand's marriage.

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