Mirta Francisca de la Caridad Díaz-Balart y Gutiérrez (born September 30, 1928) was Fidel Castro`s first wife, daughter of Rafael José Díaz-Balart and wife América Gutiérrez. She was a fellow student at the University of Havana, studying Philosophy, when Fidel married her. She was the daughter of a prominent Cuban politician and mayor of the town of Banes.

They married on October 11, 1948 and divorced seven years later (while Castro was in exile) in 1955. They had one child, a son, Fidel Ángel "Fidelito" Castro Díaz-Balart, born on September 1, 1949. After the divorce, Castro was granted custody of their son and Mirta remarried Dr. Emilio Núñez Blanco, the son of a former Cuban Ambassador to the UN, Emilio Núñez Portuondo (now deceased). A story in the October 8, 2000 [1] 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.

Díaz-Balart reportedly returned to Havana in 2002 to live with Fidelito and his family.[2]

Mirta Díaz-Balart is the aunt of current Republican and anti-Castro U.S. Congressmen Lincoln Diaz-Balart and Mario Diaz-Balart and sister of the painter Waldo Diaz-Balart and the late Rafael Diaz-Balart. She has two daughters by her second husband, Mirta and América Silvia Núñez Díaz-Balart, both residing in Spain with their families. She has numerous grandchildren.