A frat boy caught on video allegedly beating and robbing a woman in a Brooklyn subway station was easy to catch — he was wearing a hoodie with the fraternity’s Greek letters and his nickname, sources said yesterday.

Aidan Folan, who went to St. Francis College, was ratted out by brothers from his fraternity when they saw the video of him allegedly pummeling and kicking Dina Perez, 56, at the 18th Avenue F station at around 2:40 a.m. on March 9, the sources said.

Folan, 21, wore an Alpha Phi Delta hoodie with custom lettering that reads “Stugotz 27.”

The Italian slang roughly translates to testicles and is so loved by the suspect that he also chose it for his Facebook page, the sources added.

A fraternity brother said he immediately recognized the letters and figured out that Folan, a member in bad standing, received it during the one year he spent at St. Francis in Brooklyn Heights.

That brother immediately called the NYPD’s Crime Stoppers hot line and gave detectives every bit of information the group had on Folan, including his Bay Ridge address, which led to the suspect’s capture.

He was identified in police lineups yesterday.

“Being human beings, we felt compelled to do that,” the fraternity member said. “I think any human being would feel compelled. We were just appalled.”

Facebook photos show Folan mugging it up in his favorite sweat shirt. Hundreds of comments have been added by strangers who are outraged.

The fraternity has also received hundreds of angry e-mails from some of its 22,000 members across the country.

“Our thoughts, prayers and sympathy go out to Ms. Perez as she recovers from this ghastly act,” said the fraternity member who called cops.

“The alleged actions that Mr. Folan is being charged with are heinous and completely repugnant to the membership and tradition of Alpha Phi Delta fraternity. The video shows brutal and cowardly actions against Ms. Perez.”

The group was founded at Syracuse University by Italian-Americans fighting discrimination in 1914 and places importance on philanthropy.

The member who called cops said the crime was “disgraceful, infuriating, disconcerting and inhuman.

“If he’s found guilty, we will immediately expel him — not that it’ll mean anything to someone who did that,” he said, while calling for the strictest punishment under the law.

“We are embarrassed that he was a part of our brotherhood.”