A prominent Cuban-American businessman who targeted fellow graduates of his alma mater, Belen Jesuit Preparatory School, was charged Wednesday with fleecing millions of dollars from hundreds of people in an investment scheme that collapsed with the real estate bust.

Gaston E. Cantens, 73, described by victims as “Miami’s little Madoff” in reference to the notorious Wall Street Ponzi schemer, has already signed an agreement with federal prosecutors to plead guilty to one count of conspiring to commit fraud.

And like Madoff, Cantens preyed upon a close circle of friends who trusted him without thoroughly checking his rosy assurances about his company, Royal West Properties, and its financial dealings.

Cantens duped investors by promising them lucrative returns and that their investments would be guaranteed by properties or mortgages that acted as collateral, according to a plea agreement he signed last month.

But he often used the same pieces of property, sold in Southwest Florida, as purported collateral. For example, in early 2008, he assigned a piece of property to Belen Jesuit as collateral that he also used for two other investors later that same year.

The scheme didn’t stop there: “By 2008, Cantens knew that Royal West was paying existing investors with new investors’ money,” the plea agreement says.

“Despite this, Cantens fraudulently assured new and reinvesting investors in late 2008 that their investment payments were coming from mortgage payments and other legitimate real estate transactions.”

Court documents show that more than 150 investors — including Belen Jesuit in West Miami-Dade — lost a total of $47 million by sinking $135 million into Cantens’ company between 2003 and 2008.

Representatives for the private boys’ preparatory school, which was founded here in 1961 but traces its roots to Cuba, declined to comment.

Cantens graduated from Belen in 1957 before emigrating to Miami. (Fidel Castro, Belen’s most famous alumnus, graduated from the Havana school in 1944.)

Cantens faces up to five years in prison. He might receive less than the maximum term because he is accepting responsibility for his crime rather than going to trial. Under the plea agreement, Cantens is being held liable for investment losses ranging from $7 million to $20 million, involving more than 50 victims.

But the profile of those victims will likely weigh against him before U.S. District Judge Kathleen Williams.

The U.S. Attorney’s Office will argue at his sentencing “that the court should consider how the defendant targeted a religious institution and vulnerable elderly investors,” federal prosecutor H. Ron Davidson wrote in the plea agreement.

Cantens’ lawyer, Bruce Lehr, said his client decided not to continue fighting the charges against him.

“After nearly 30 years in business, unfortunate circumstances caused him to make serious mistakes for which he is accepting full responsibility,” Lehr said. “Throughout this process, it was always clear that Mr. Cantens’ actions were not for personal gain but were actions attempting to save a struggling real estate business at the time.

“Mr. Cantens is extremely remorseful for his actions and understands that they were not the proper course to follow under the circumstances,” he said.

In 2010, Cantens and his wife, Teresita, 75, were accused in a civil complaint brought by the Securities and Exchange Commission of defrauding investors. SEC officials alleged the Cantenses were not registered with the federal government to make securities offerings.

The couple “used their prominent standing in a close-knit Cuban-American community to ruthlessly exploit vulnerable elderly investors who trusted them with their life savings,” Eric I. Bustillo, director of the SEC’s Miami office, said in a statement.

Last year, a final judgment in the SEC case was filed against the Cantenses, ordering them to pay back more than $5.3 million in illegal profits. But the penalty was not collected because of the couple’s inability to pay.

Teresita Cantens has not been charged in the criminal case filed in Miami federal court.

The couple’s son, Gaston I. Cantens, is a former state representative and vice president of the Florida Crystals Sugar Co.