The leader of the upstate sex cult Nxivm recruited a 15-year-old girl from Mexico as his first “sex slave,” prosecutors revealed Tuesday.

Details of the beginnings of DOS, the secret sorority of sex slaves allegedly created by Keith Raniere, were laid out as his sex-trafficking trial got under way in Brooklyn federal court.

“This was organized crime. Keith Raniere was an organized crime boss,” prosecutor Tanja Hajjar told the jury of eight men and four women in her opening statements.

She explained how Raniere, who billed himself as a self-help guru, brought the teen, Camilla, and her two sisters from Mexico in 2005 to live in New York.

He promised to mentor the young women as part of his Albany-area self-empowerment group Nxivm, Haijar said.

But “the defendant wasn’t interested in mentoring,” Haijar said. “Instead, he had sex with all three daughters.”

Raniere began sleeping with Camilla, the youngest sister, at age 15, and nicknamed her “Virgin Camilla,” Hajjar alleged.

The charming Nxivm founder soon pitted “sister against sister” — and retaliated against one of them, Daniela, after learning she had feelings for someone else. Raniere, 58, shut her in a “room for two years” before banishing her to Mexico altogether, according to the prosecutor.

Camilla, meanwhile, was the linchpin in the formation of Raniere’s alleged sex cult’s subgroup, DOS — a Latin acronym that roughly translates to “master of the obedient female companions.”

The alleged slave victims had to vow “a lifetime of obedience, a lifetime of commitment” to Raniere and also submit damaging collateral that could be used to blackmail them, said Hajjar.

“In the defendant’s own words, he wanted his DOS slaves to be branded with his monogram,” she added.

As Raniere’s first “slave,” Camilla was urged to recruit other slaves to sleep with him.

One recruit, an actress named Nicole in her 30s, was introduced to Raniere while “blindfolded and tied to a table,” Hajjar said.

“A third person came into the room and started performing oral sex on her,” she said. “That third person was Camilla.”

Raniere — known within Nxivm as grand master “Vanguard” — showed little emotion as he scribbled notes during Hajjar’s opening statements.

The trial is expected to last about six weeks.

Prosecutors said two of Raniere’s co-defendants, “Smallville” actress Allison Mack and Lauren Salzman, served as master slaves. They are among five women who have also been charged alongside Raniere, including Seagram’s liquor heiress and Nxivm bankroller Clare Bronfman.

All five co-defendants have pleaded guilty — but it’s not clear if any will testify against Raniere.

Several other alleged slaves are expected to take the stand but will testify using only their first names.

Raniere has been behind bars since his arrest in March 2018 after fleeing to Mexico with Bronfman.

He has pleaded not guilty to various charges, including racketeering conspiracy involving acts of child sexual exploitation and possession of child pornography. The defense says the relationships were consensual.

Prosecutors are expected to introduce a trove of evidence against the accused cult leader, including child pornography images seized from his upstate New York home.

If convicted, Raniere faces up to life in prison.