Castro Diaz-Balart, also known as "Fidelito" because of how much he looked like his father, had initially been hospitalized for depression and then continued treatment as an outpatient.

"Castro Diaz-Balart, who had been attended by a group of doctors for several months due to a state of profound depression, committed suicide this morning," Cubadebate website said.

Fidelito was born in 1949 out of his Castro's brief marriage to Mirta Diaz-Balart before he went on to topple a U.S.-backed dictator and build a communist-run state on the doorstep of the United States during the Cold War.

The dictator died in November, 2016, aged 90.

Castro Diaz-Balart, a nuclear physicist who studied in the former Soviet Union, had been working as a counsellor to the Cuban Council of State at the time of his death.

He had been head of Cuba’s national nuclear programme, and spearheaded the development of a power plant on the island.

But, Cuba brought the plans to a grinding halt following a lack of funding and cut ties with ex-Soviet nations.

Castro Diaz-Barat then disappeared from public view.

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