Oren Alexander, the luxury real estate broker accused of serial sex assault alongside his two brothers, appeared to boast about gang rape in a disturbing yearbook photo.

The photo, obtained by NBC 6, shows a young Alexander — whose wife is due with their first child any day now — bragging about “riding my first ‘choo-choo’ train” in an apparent reference to gang rape.

Federal prosecutors have said the Alexander brothers’ sick history of sexual violence began at Michael Krop Senior High School in Miami.

“Each of the victims that the government has interviewed from this period reported hearing that individuals involved — including Tal Alexander— talked about the assaults at school, boasting about ‘running train’ on their victims and saying they wanted to ‘do it again,’” the prosecutors wrote in a court filing arguing for them to be held without bail.

Oren Alexander, 37, is charged with his twin, Alon Alexander, and their older brother Tal Alexander with drugging and raping dozens of women over more than a decade — by luring their victims with their wealth and prestige, prosecutors said.

Tal, 38, and Oren, bigwigs in high-end real estate who helped broker the sale of a record-setting $240 million penthouse overlooking Central Park, worked with Alon to use “the promise of luxury experiences, travel, and accommodations to lure and entice women to locations where they were then forcibly raped or sexually assaulted,” federal prosecutors alleged Wednesday.

Alon has been an executive at the private firm Kent Security, founded by the brothers’ parents, Orly and Shlomy Alexander.

The trio was arrested at separate residences in and around Miami Beach on Wednesday morning and are charged federally with conspiracy to commit sex trafficking and sex trafficking by force.

Many of the sexual assaults involved “multiple men,” and took place in Manhattan, New York, and Miami, Florida, where their residences and businesses were based, the indictment said.

Several female victims were drugged with the date rape drug GHB, and other assaults included cocaine and psychedelic mushrooms, according to their indictment.

Oren and Alon appeared in a Florida courtroom Thursday wearing suicide vests and were ordered held without bond by Circuit Judge Mindy Glazer on Thursday.

Their older brother, who has also been charged with heinous crimes, 38-year-old Tal Alexander, will have a detention hearing on Friday.

Tal rents an apartment on Midtown’s famed “Billionaire’s Row,” and Oren and Alon live in “high value” properties in Miami Beach with “direct access to water” and “private docks,” the feds wrote in a court filing.

Shlomy Alexander flashed a bizarre smile and said “great” when asked by a reporter how he was doing following his 37-year-old sons’ arrests, according to NBC 6 footage.

All three brothers will eventually be extradited to Manhattan federal court.

Each faces 15 years to life in prison if convicted.