Fidel Castro was so desperate about Cuba's financial situation at the start of the 1980s that he turned to a banker from the country he hated the most, the United States, to get advice on restructuring the country's heavy debt load.

"It was the year the of Marielitos"—the 1980 Cuban boatlift—"and he was under a lot of strain to be able to service the debt to the European banks who had lent to him, and also to some Canadian banks," said Bill Rhodes, a former Citigroup executive and author of "Banker to the World." Rhodes was the bank's point person on Latin America for decades.

Rhodes told CNBC he agreed to the meeting at the behest of then-Nicaraguan leader Daniel Ortega, who knew Rhodes because he was representing the banks in the negotiation of the Central American country's debt restructuring.

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"He asked to see me. I didn't ask to see him," Rhodes said.

During Rhodes' meeting with Castro, the Cuban leader made some startling admissions.

Among them: Castro told Rhodes he regretted kicking the International Monetary Fund out of Cuba in his early days of the communist revolution.

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Rhodes recounted that Castro told him Cuba should have stayed a member not only of the IMF, but also the World Bank and the Inter-American Development Bank. "And he said that was a poor decision, because they're institutions that could have helped Cuba, you know, in our economic problems."

The IMF, based in Washington, has long been controversial and never more so than recently due to its involvement in the Greek financial crisis. The current leaders of Greece have criticized the institution and tried to eliminate its involvement in the Greek economy.