Its designation commemorates the fact that the brother of D. João IV, the infant D.Duarte (1605-1649), who after beating himself in the service of the Emperor of Germany during the Thirty Years War, was betrayed and closed in Milan fortress, for the revenge of Philip IV of Spain. In prison he died, all diplomatic efforts were made to free him. The Portrait of Infante D. Dute, displayed on the fireplace, was painted by João Reis in 1951.

The tapestry that represents the Roman general Decius Mus saying goodbye to his Lictores, was woven in Brussels in the 17th century, by the tapestry Franz van Hecke, on a card by Peter Paul Rubens.

The two royal marble busts represent, on the right, Queen Elisabeth of Belgium (1876-1954), by Victor Rousseau (1865-1954), on the left, Queen D. Amélia, by Tomás Costa (1861-1932). The furniture of pau-santo, dates from the 17th and 18th centuries; on the buffets there are two sculptures by Clodion (1734-1814) Fauna and Fauneza.