Career
John II sought to limit the power of the upper nobility, which had increased greatly during the reign of John"s father Afonso V of Portugal. He was imprisoned, tried and executed in Évora. On two occasions, the king’s life was in danger and as Diogo of Viseu remained the leader of the upper nobility against the King’s policies, John II accused him of high treason and personally killed him.
After the execution, King John II called the duke’s younger brother, Infante Manuel of Viseu, and showed him his brother’s body.
Duke Diogo never married, but when he was quite young he visited the Crown of Castile, where he had a love affair with Doña Leonor de Sotomaior y Portugal (great-granddaughter of King Pedro I of Portugal). With her he had a natural son, Afonso de Portugal.
Afonso’s daughter and heir, Beatrice of Lara, married the 3rd Marquis of Vila Real.