Duke of Frías
He was the son of Andrés Manuel Alonso Téllez-Girón Pacheco y Toledo and María Portería Fernández de Velasco y Pacheco. His mother was the daughter of Bernardino Fernández de Velasco, 11th Duke of Frías, who was succeeded by his brother Martín Fernández de Velasco y Pimentel. When the 12th Duke died in 1776 without children, the title of 13th Duke of Frías went to Diego, who called himself since then "Diego Fernández de Velasco y Pacheco".