Fidel Castro had around 11 children but the Canadian prime minister was not one of them.
The Trudeaus were close to Fidel Castro and exchanged letters. However, no official meetings took place until 1976. Justin's mother, Margaret, was always under scrutiny by the press as she was the wife of prime minister. There is no evidence to support the notion that Margaret Trudeau met Castro before 1971. The timeline also supports that she gave birth to Justin just ten months after her wedding with Pierre, on Christmas Day in 1971.