The El Escorial Conspiracy (2008)

spanishcastlemoviemagic.com

Despite being a Spanish production, the film was made in English, with some obvious dubbing of some of the Spanish actors.
As the title suggests, many interiors and exteriors were filmed in the royal Escorial palace, just outside Madrid, including the library and throne room.
Also near Madrid, the old Monastery of Talamanca de Jarama, now privately owned and used in many films and other functions, is the scenario of the assassination at the beginning.
Filming also took place in Segovia, at the Alcázar Castle and La Granja royal summer palace, as well as the forest of Valsaín, where the Constable meets the Moorish girl, who is washing clothes in the stream.