Juanita Castro initially supported her brother’s 1959 overthrow of the Batista dictatorship, but quickly grew disillusioned.
In a memoir released today by Santillana USA, the 76-year-old says the wife of the Brazilian ambassador to Cuba persuaded her to meet a CIA agent during a trip to Mexico City.
Castro says in the book she agreed then to help the CIA gather information, but refused to accept money for it.
Her home became a sanctuary for anti-communists before she fled the island in 1964. She eventually settled into a quiet life in Miami and ran a pharmacy until 2007.