Citigroup executive and author of "Banker to the World" Bill Rhodes revealed some of the biggest financial regrets of revolutionary and Cuban leader Fidel Castro.

When Castro was very desperate from Cuba's financial turmoil during the start of 1980, he asked for advice on restructuring the country's debt problems from a banker in the United States - Rhodes.

One of Castro's biggest regrets, according to Rhodes, is kicking out the International Monetary Fund out of Cuba during the early days of the revolution. IMF has been a very controversial institution, especially in its involvement with the recent Greek financial crisis.

Another big regret from Castro is assigning Ernesto "Che" Guevara to manage the Cuban central bank. According to Rhodes, Castro told him that Guevara knows nothing about finance and banking.

As the most prominent figure of the Cuban revolution, Guevara became the chief of the Cuban central bank in 1959. By September 1960, he seized all the American banks in Cuba, including the National City Bank of New York (Citigroup), the National Bank of Boston (Bank of America), and Chase Manhattan (JPMorgan Chase). Because of the seizure, all these banks now have outstanding claims against the Cuban government.

Meanwhile, the US embassy reopens in Cuba last Friday for the first time in 54 years. John Kerry landed in Cuba for the flag raising ceremony. Washington also seeks to resolve billions of dollars worth of American claims that goes back to half a century ago.

These claims are due to property confiscated after the revolution. Kerry said during the ceremony that even though the US embargo still exists in Cuba, the White House favors the Congress lifting the restrictions.   

Even before the US embassy reopened in Cuba, there is a small group of investors waiting and hoping to finally get paid after Cuba stopped paying what it owed 15 years ago.