Diaz-Balart, 68, the oldest son among Fidel’s 11 children, was being treated by a group of doctors for the depression he suffered in the final months of his life, various Cuban media outlets report. Diaz-Balart was a doctor of sciences, the Vice President of the Academy of Sciences of Cuba, and served as scientific advisor to the Council of State.

Diaz-Balart was the only son of Fidel and his first wife Mirta Diaz-Balart, who has  survived both her late husband and son at 89.

“Fidelito,” as he was popularly known in Cuba, was the author of 11 books and over 150 scientific articles on nuclear physics, energy and its relation to environmental studies. In a 2013 interview with RT, he said his interest in the sciences was boosted by the revolution, and that he had studied nuclear physics in the former Soviet Union.