Juanita Castro, sister to Raúl and Fidel, shocked the world Monday with the revelation that for many years she had been working with the United States Central Intelligence Agency.

In a new memoir, "Fidel and Raúl, My Brothers: The Secret History," Juanita, now 76, reveals herself and her CIA code-name, Donna, in what she calls her family's greatest secret. Juanita fled Cuba in 1964.

"She made the revelation to a Spanish-language television channel (Univision-Noticias 23) in Florida Sunday," Voice of America news reported. She was interviewed by Maria Antonieta Collins, who co-authored Juanita's book.

"There had been widespread speculation for many years about Juanita's recruitment, said Brian Latell, a former CIA analyst who is now a senior researcher in Cuba studies at the University of Miami, and author of the book After Fidel," The Guardian noted. "'She was considered a success by the CIA. It was very pleased with her, especially after she left Cuba. She was very outspoken and played a critical propaganda role in traveling around Latin America. She had quite an impact in Chile's 1964 election.'"

For her service -- sending secret messages using selected songs over clandestine radio, or packing coded messages in cans of food -- Juanita said she accepted no payment. Instead, she insisted that Fidel and Raúl had betrayed Cuba and become despots.

"In the book, Juanita Castro says she was approached on behalf of the CIA by Virginia Leitao da Cunha, wife of the then-Brazilian ambassador in Havana, Vasco Leitao Da Cuhna, who would later go on to serve as Brazil's foreign minister," The Miami Herald added.

Juanita left the country on a visa to Mexico, where she quickly went public in her opposition to the regime. According to her book, Raúl had claimed that the government had opened a file and was investigating her for undermining Fidel's authority.

"She does not elaborate in the interview on her activities except to say that she sheltered and helped people persecuted by the government," USA Today reported.

Juanita has not spoken to her brothers since 1963.