Career
She was a fellow student at the University of Havana, studying philosophy, when Fidel married her. They had one child, a son, Fidel Ángel "Fidelito" Castro Díaz-Balart, born on September 1, 1949. There is a documented story of the rescue of Mirta"s son from the captors of Fidel Junior.
Mirta remarried to Doctor Emilio Núñez Blanco, the son of a former Cuban Ambassador to the United Nations, Emilio Núñez Portuondo.
A story in the October 8, 2000, edition of the Miami Herald claimed that she was then living in Spain and that occasional visits to Cuba had been arranged by Raúl Castro, her former brother-in-law.
She is the sister of the painter Waldo Diaz-Balart and the late Rafael Diaz-Balart. She has numerous grandchildren.