What is de aguirre?

Some articles on de aguirre, de:

Mariana De Aguirre
... Mariana de Aguirre y Boza was First Lady of Chile as wife of Chile's late-1829 President Francisco Ramón Vicuña with whom she had six children ... She was born in Santiago, Chile to father José Santos de Aguirre y Díez de Aséndegui, 2nd Marquis of Montepío, and mother Antonia de Boza de Lima y Andía-Irarrázaval ...