Tello Alfonso, Lord of Aguilar de Campoo

Tello Alfonso of Castile (1337–October 1370) was the seventh of the ten illegitimate children of Alfonso XI of Castile and Eleanor of Guzman. He was a prince of Castile and First Lord of Aguilar de Campoo. In Spanish he is known as Tello de Castilla, Infante de Castilla; Señor de Aguilar de Campoo, de Vizcaya, de Castañeda y de Lara.

He was born in Seville. He participated along with his brothers in the struggles against the despotic rule of his half-brother Pedro of Castile also known as Pedro the Cruel.

In 1353 he married Juana of Lara (daughter of Juan Núñez III de Lara), but she was reportedly murdered in 1359, on order of King Peter (Pedro the Cruel). Tello and Juana had no legitimate children. It is reported that Tello kept news of her death secret in order to maintain possession of her dowry.

Tello had many illegitimate children.

• Juan Tellez de Castilla, Segundo Señor de Aguilar de Campoo, (1355-1385). He died at the Battle of Aljubarrota. From his marriage to Leonor de la Vega arise the Marquesses of Aguilar de Campoo (Grandees of Spain).
• Afonso Tellez de Castilla, b. 1365
• Pedro Enríquez de Castilla, Señor de Camporedondo, b. 1370
• Fernando Tellez de Castilla, died young.
• Constanza Tellez de Castilla.
• Maria Tellez de Castilla.
• Isabel Tellez de Castilla.
• Elvira Tellez de Castilla.
• Juana Tellez de Castilla.
• Leonor Tellez de Castilla, died young