Seagram’s liquor heiress Clare Bronfman used her family fortune to buy an entire island, the private plane to get there — and, the feds say, to bankroll a sex cult.

On Tuesday, the 39-year-old — who is worth roughly $200 million — was busted on racketeering charges for her role in running Nxivm, alongside three other high-ranking members.

The arrests are part of an ongoing federal investigation into the group’s leader, Keith Raniere, and his right-hand woman, former ​”Smallville​”​ star Allison Mack.

Raniere and Mack are charged with sex trafficking and conspiracy for allegedly coercing women into joining a secretive master-slave society within Nxivm — where “slaves” were forced to pleasure Raniere, have his initials permanently branded onto their skin and perform free labor.

In Brooklyn federal court Tuesday, a gaunt Bronfman pleaded not guilty to allegations she conspired with Raniere to steal email passwords from his “perceived enemies,” racked up charges on the credit card of his dead ex-girlfriend and laundered money to help a non-citizen fraudulently gain entry to the US.

​Bronfman was part of an “inner circle” of loyalists who “committed a broad range of serious crimes from identity theft and obstruction of justice to sex trafficking, all to promote and protect Raniere and NXIVM,” U.S. Attorney Richard Donoghue said in a statement.

​She faces up to 20 years behind bars if found guilty — a stunning change in circumstances for a woman who could have had anything in the world she wanted.

Bronfman and her older sister, Sara, are the daughters of late Canadian billionaire Edgar Bronfman Sr. and a British barmaid-turned-socialite 20 years his junior. She was his third of four wives — and they were the youngest of his seven kids.

Backed by hefty trust funds, party girl Sara spent her 20s flitting around the globe trying to find herself, while the more serious Clare pursued a career as an elite equestrian show jumper.

Sara was first to fall into Nxivm’s thrall, taking one of its self-help workshops in 2002 at age 25, when a marriage to an Irish jockey fell apart after seven months, according to a Macleans report.

She soon roped in Clare, then 23, who hoped the life coaching organization could help her in her quest for a spot on the US Olympic equestrian team.

Instead, they became full-time devotees of Raniere — known as “Vanguard” in the organization, where followers earn colored sashes as they coughed up more money to ascend the ranks.

“Coming from a family where I’ve never had to earn anything before in my life, [it] was a very, very moving experience for me to be awarded this yellow sash. It was the first thing that I had earned on just my merits,” Sara Bronfman explained in a 2003 Forbes article.

Clare made it to the Olympic trials in 2004, but gave up on horse riding after Raniere told her she had better things to do with her time, an insider told Vanity Fair.

At first, the sisters convinced their elderly dad to take Nxivm’s $10,000 “VIP” course — but he soon soured on the organization, and became estranged from his daughters, when he heard Clare had lent Nxivm $2 million, according to a Vanity Fair report.

“I think it’s a cult,” he later told Forbes.

The sisters quickly ascended to the top of the Albany-based organization — thanks more to their bank balances than any business acumen — and that $2 million had ballooned into as much as $150 million by 2010, including $66 million that Raniere lost betting in the commodities market and $11 million on a private jet, according to Vanity Fair.

Sara eventually married a wealthy Libyan businessman, moved abroad with him and had kids — but Clare has remained in Raniere’s inner circle.

Nxivm’s intense self-improvement classes had, at one point, earned it thousands of adherents, including some with Hollywood ties. They included Nicki Clyne, an actress who appeared on “Battlestar Galactica”; a son of former Mexican President Carlos Salinas de Gortari; and India Oxenberg, a daughter of “Dynasty” actress Catherine Oxenberg.

​But Nxivm expanded well beyond its beginnings as merely a sketchy executive self-help organization.​ Indeed, from its beginnings in the late 1990s, prosecutors allege that Raniere kept “a rotating group of 15 to 20 women” from the group as his personal harem.

​​But in 2015, the​ feds allege​,​ things got seriously twisted when he and Mack created a secret master-slave “sorority” within Nxivm called “The Vow” or “DOS,” prosecutors allege.

Mack duped women from Nxivm into joining and handing over damaging collateral by saying it was a women’s empowerment group — then groomed them as slaves for Raniere.

Clare Bronfman says she was never in the society, but prosecutors say she still aided Raniere in his criminal dealings by, among other things, continuing to dip into the $8 million bank account of one of Raniere’s former lovers after she died of cancer last year.

That woman, Pamela Cafritz, was the daughter of DC A-listers William and Buffy Cafritz.

“Keith Raniere’s girlfriend had been paying for his expenses, and when she died, they kept using the card for expenses,” Bronfman’s defense attorney, Susan Necheles, said in court Tuesday.

Necheles — a high-powered lawyer who, among others, has represented disgraced Mayor Bill de Blasio donor Jona Rechnitz — added that the allegations about stealing passwords are a decade old.

“She had been having a fight with her father, and allegedly had someone break into her father’s computer,” said Necheles.

The judge set a stunning $100 million bail — secured against $50 million of her assets — and placed Bronfman under house arrest, agreeing with prosecutors that she is a significant flight risk thanks to her huge wealth, private jet and an island she part-owns in Fiji.

She’s also forbidden from contact with other members of the cult until details of the bail are finalized Friday.

When Necheles objected, given that Bronfman’s friends are also Nxivm members, Judge Nicholas Garaufis snapped.

“Doesn’t she have Netflix?” he responded irritably. “Let her watch Netflix between now and Friday.”

“If you’re telling me she can’t be staying away from people who are part of this alleged criminal organization for a couple days, maybe I’m making the wrong decision.”

One of the co-signers of the bail is Sara Bronfman — who will have to fly back from where she now lives in France by Friday. When Necheles said that might be tough, given she has two young kids, Garaufis said too bad.

“She can manage,” he snapped. “Tell her she can bring the kids to New York. They can go see a play — make suggestions.”

​​Garaufis, looking over the financial documents to support her bail application, asked, “Her Fiji properties are listed at $40 million?”

“It’s an island,” Bronfman’s attorney explained.

“She bought an island?” Garaufis marveled.

“It’s a resort she’s developing in Fiji,” Necheles said. “$47,000,000 is what she paid for it.”

Also arrested Tuesday was the cult’s co-founder, Nancy Salzman, her daughter Lauren, and Kathy Russel, Nxivm’s longtime bookkeeper, for their alleged roles in aiding Raniere.

Lauren — who’s been accused by former “slaves” of being one of the “masters” in the group — is alleged to have committed forced labor, extortion and wire fraud.

Prosecutors allege that she kept a former sexual partner of Raniere’s confined to a room for two years after the woman developed feelings for another man, threatening to dump her in Mexico with no ID if she didn’t comply.

Lauren eventually made good on the threats, they claim.

All three were arraigned in Albany, where they pleaded not guilty.

With Post wires​