Sancho Alfonso, 1st Count of Alburquerque

Sancho Alfonso de Castilla (1342–1374) is known in Spanish as Don Sancho Alfonso de Castilla, Infante de Castilla, I conde de Alburquerque.

He was the ninth of the ten illegitimate children of King Alfonso XI of Castile and Lady Eleanor de Guzmán.

He was born in Seville. He participated in a revolt of the Castilian nobles against the despotic rule of his brother, Pedro of Castile.

In 1373 he married Beatrice of Portugal, daughter of Peter I of Portugal and Inês de Castro. They had two children: Fernando Sánchez, 2nd Count of Alburquerque, and Eleanor of Alburquerque, who married Ferdinand I of Aragon.

He also had an illegitimate daughter, Leonor Sánchez de Castilla, who married Fadrique de Castilla y Ponce de Leon, illegitimate son of Henry II, King of Castile.