Fidel Ángel Castro Díaz-Balart is said to have suffered from depression.
He had been treated by a group of doctors for several months due to deep depression.
He took his life this morning.
State television said he had been receiving medical treatment as an outpatient in recent months, following a hospital stay.
The first-born son of the late president was nicknamed “Little Fidel”, because of the family resemblance.
He was a Nuclear Physicist, trained by the former Soviet Union.
At the time of his death, he was a Scientific Adviser for the Cuban Council of State and he served as Vice President of Cuba’s Academy of Sciences.
He headed the island’s nuclear programme from 1980 to 1992, before it was suspended after the Soviet Union’s collapse.