To the CIA she was Donna: a Cuban spy who hid documents inside cans of food and sent secret messages via a clandestine radio and two tunes – a waltz and a song from the opera Madame Butterfly.

Today, Donna was revealed to the rest of the world as Juanita Castro – the sister of Fidel and Raúl, rulers of Cuba and legendary conquerors of US espionage efforts – when she blew the whistle on her career as a CIA agent.

The rogue sibling revealed extraordinary details of her hidden identity in a memoir, Fidel and Raúl, My Brothers: The Secret History, which could force a partial revision of the CIA's role in Cuba. For half a century its efforts against Fidel were considered fiascos, prompting recrimination and ridicule. It tried and failed to kill him, tried and failed to invade Cuba, and tried and failed to foment revolt.



Cuba was just 90 miles off Florida, but its ruler was thought too wily and his regime too hermetic for the hapless American spies. Now, in what she describes as the family's best-kept secret, Juanita has revealed that the CIA infiltrated the world's most famous communist clan.

The 76-year-old Miami exile recounts how she sheltered government opponents in her Havana home, among other subversive acts, before leaving Cuba in 1964 and publicly denouncing Fidel and Raul as despots, a bombshell which damaged the revolution's image in Latin America.

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. "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 travelling around Latin America. She had quite an impact in Chile's 1964 election."

Juanita initially hailed the revolution's 1959 triumph over the US-backed dictator, Fulgencio Batista, and supported its social programmes by working in health clinics. But executions of opponents and the squelching of democratic hopes disillusioned her. She was already discreetly aiding dissidents when, according to her book, the wife of the Brazilian ambassador in Havana, Virginia Leitao da Cunha, asked her to meet a CIA agent, Tony Sforza. Sforza had previously worked on a Cuba-related CIA project known as Operation Mangosta.

"Many of our men are working there [in Cuba] and run the risk of being discovered," Sforza told her at the Hotel Camino Real in Mexico City. "The mission involves protecting them and helping them move from one place to another with as much security as possible, finding them places to stay in houses that are safe." Her family links gave her invaluable access to prisons, he added.

Juanita agreed to take on the code name Donna and gave Sforza two tunes that, when played over a clandestine radio, would signify that she had, "or did not have", a message. One of them was Madame Butterfly; the other was a waltz, Fascinación.

Her first mission was to take money, messages and documents back to Cuba from Mexico, hidden inside cans of food. She also carried a codebook back with her and, after receiving a shortwave radio, persuaded two former school friends to aid her. She says she refused to take part in anything that would cause bloodshed and refused payment for her services.

Her cooperation was a rare cold war success for spymasters tasked with toppling the Soviet Union's tropical ally. The Kennedy White House authorised many CIA assassination attempts – ensuing decades racked up 638 efforts, according to one estimate - as well as the disastrous Bay of Pigs invasion by exiles.

Juanita held no senior government rank and was not thought to be privy to official secrets, but her enlistment by the US, if verified, dents the reputation of Cuba's formidable intelligence service.

Raúl, the then defence minister and now president in place of the ailing Fidel, knew of their sister's wayward political views in 1964, but still approved her trip to Mexico, where she defected.

The revelation that the CIA appeared to have been pulling strings, and not simply applauding, is likely to annoy Cuba's government, even though the events were so long ago, said one western diplomat in Havana. "Under Obama, relations between the US and Cuba are going in a slightly better direction. This won't help that process."

State media will report the news if authorities calculate they can turn the story to their advantage, said the diplomat. "Even if the media here ignore it, the story will do the rounds among the public. But it's history, and Cubans are used to not being surprised by anything."

This week the UN will take its annual vote against the US embargo of the island, a 49-year-old policy widely deemed anachronistic and unjustified.

It is unclear why Juanita, who spent the past two decades quietly working in a pharmacy in Miami, waited until now to tell her story. She began working on the book, published by Santillana, with her co-author, the journalist Maria Antonieta Collins, in 1999, but then stopped and resumed only this year.

Published simultaneously in the US, Mexico, Colombia and Spain, the memoir had Harry Potter-style secrecy and was kept in sealed boxes and secured pallets to avoid leaks.

Family business

• "Fidel always had a strong personality … He was always the leader of the brothers. He got on well with all his siblings, though he was never as affectionate, attentive or kissy as the others."

• "Ramon, Fidel and Raul were all very independent and different to each other. Raul was mother's favourite, perhaps because he was the youngest. She called him "my little muse" and he, in turn, was always very close to her."

• "Fidel's radical conversion to communism was not made from political conviction but simply because he needed power, which is the only thing that he has ever cared about. Without the Russians he would not have been able to carry on."

• Juanita believes, however, that Eisenhower missed a chance to change the history of Cuba by failing to meet Fidel Castro when he visited the US shortly after the revolution in April 1959. Eisenhower instead sent his vice-president, Richard Nixon. "That was taken in Cuba as if they had turned their back on Fidel," she explains.

"The polls at that time showed that 90% of Americans supported Fidel," she continues. "That decision put an end to any chance of reconciliation. If things had not happened that way Fidel might not have turned to the Soviet Union."