Guests danced the night away Saturday at the Red Cross ball held at Donald Trump’s Mar-a-Lago mansion in Palm Beach, Fla. (CAPEHART)

Mar-a-Lago, the most beautiful mansion on this perfectly manicured island, is owned by Donald Trump, who built a 20,000-square-foot addition inspired by Versailles and turned it into this town’s most glamorous party palace. The International Red Cross held its 59th annual ball there Saturday night, complete with Britain’s filthy-rich Duke of Westminster, ambassadors, honor guards and 500 of Palm Beach’s most philanthropic one-percenters.

The elephant in the Donald J. Trump Grand Ballroom was not, in fact, in the room. The GOP front-runner, a regular at the prestigious white-tie ball, was in New Hampshire duking it out at the last Republican debate before Tuesday’s primary.

“Tonight I’d like to honor possibly our future president: Mr. Donald Trump,” honorary ball chairman Patrick Park told the crowd. “A little applause for him! We love you, Mr. Trump!”

There was a little applause — and a smattering of lusty boos. Even under his own roof, Trump is a polarizing figure.

“He’s the talk of every conversation here,” said Stuart Bernstein, a loyal Republican and former ambassador who splits his time between Washington and Palm Beach. “I find that most people like him, but he makes them nervous. They’re frustrated and angry that the system is broken. We need a strong leader — that’s what they like.”

Donald Trump and wife Melania Trump attended last year’s Red Cross ball at his Mar-a-Largo in Palm Beach, Fla. (CAPEHART/Getty Images)

Palm Beach has been carefully watching Trump since he splashed down 30 years ago in this exclusive enclave and bought the historic Mar-a-Lago. Before he launched his presidential bid, he spent almost every weekend here, charming and shocking the locals with both his generosity and his unapologetic self-promotion. Now his neighbors are trying to wrap their heads around the possibility that he may become the Republican nominee — or even president.

“The people who love him will still love him,” said Franklyn deMarco, owner of the popular Taboo restaurant on tony Worth Avenue. “And the people who despise him will still despise him. It didn’t make any difference with Jack Kennedy.”

The Kennedys were considered “shanty Irish” and blackballed from the most prestigious clubs, even after Kennedy was elected president. Palm Beach was founded a century ago by the barons of the Gilded Age and has maintained a strict code of understated elegance, private clubs and exclusion. No other place quite encapsulates America’s obsession with wealth, class and status. Billionaires can’t buy their way into the WASPy Everglades or Bath & Tennis clubs; old money (what’s left of it) trumps new money, even Trump’s. Social climbing is a contact sport.

Trump plays this game by his own rules. He scooped up Mar-a-Lago in 1985 for $10 million, a bargain-basement deal that still has locals kicking themselves for not buying the property themselves. The mansion, completed by cereal heiress Marjorie Merriweather Post in 1927, boasts 118 rooms on 20 acres of what is now arguably the most valuable land in Florida. After her death in 1973, Post left Mar-a-Lago to the federal government as a presidential retreat, but it was too expensive for the feds to maintain, and the property was put up for sale. Trump lived in it for 10 years, then spared no expense to turn it into his own private club.

“I’m the king of Palm Beach,” Trump told the New York Times last week.

Laurence Leamer, author of “Madness Under the Royal Palms,” has a slightly different take.

From left, the Duke of Westminster, Bonnie McElveen-Hunter, chairman of the American Red Cross, and former Stuart Bernstein, former ambassador to Denmark, at the Red Cross ball. (CAPEHART)

“He’s the king of Mar-a-Lago,” Leamer said. “But a king that can’t go next door to Bath & Tennis. These are the kind of people who don’t appreciate him.”

But where some would see rejection, Trump saw opportunity. He understood that there were plenty of people, including a very wealthy Jewish community, who could not gain entry to any other club, Leamer said. “He’s a real New Yorker in the best sense that he doesn’t have these prejudices.”

Trump turned the National Historic landmark into the most exciting private club on the island. Now the biggest name in Palm Beach walks through his property every weekend glad-handing and taking selfies with members who pay at least $100,000 to join.

At the very least, Trump is king of the Red Cross ball. This, too, was an inheritance from Post, who founded the fundraiser in 1957. It was considered the most glamorous of all the social events because Post brought down ambassadors from Washington, and the guests trotted out their white ties, biggest jewels and latest spouses. In 2005, shortly after he completed the grand ballroom for his wedding reception, Trump persuaded ball organizers to move the event from the historic Breakers hotel to Mar-a-Lago, and he has served as the larger-than-life honorary host ever since.

“It used to be men wearing white tie and decorations, the grandes dames of old-guard Palm Beach in haute couture ballgowns and family tiaras, a 20-piece orchestra playing foxtrots and rumbas,” said Washington writer Kevin Chaffee, who has attended the ball for more than 20 years.

Some in that old guard, such as 98-year-old Mildred “Brownie” McLean (she attended the first ball and 50 more since then), commend Trump for restoring Mar-a-Lago to its former glory. Others won’t step foot in the place.

In any event, the Red Cross didn’t raise $1 million Saturday night by turning people away. Party guests, who paid $1,000 and more per ticket, wandered through Mar-a-Lago’s opulent first-floor rooms and a formal receiving line before swanning down to the pool for cocktails. “If you look at the success of Mar-a-Lago and how Trump is a hands-on manager to make everything impeccable — that’s an example of how he would operate as president,” said Ron Kessler, author of “The Season: The Secret Life of Palm Beach and America’s Richest Society.”

The theme was the “Spirit of America,” with Army hospitals and actors dressed as characters from “M*A*S*H*” — a non sequitur until Loretta Swit, a.k.a. Maj. Margaret “Hot Lips” Houlihan, was introduced as part of the evening’s salute to Red Cross volunteer nurses who follow in the tradition of founder Clara Barton.

“Nurses continue to be ranked by the American people as the most trusted profession in our nation,” Bonnie McElveen-Hunter, chairman of the American Red Cross, said in her strictly nonpartisan remarks. “I believe there are probably some politicians and presidential candidates who would like the same ranking” — which elicited a sly laugh from the audience.

The dignitaries — including ambassadors from Japan, Afghanistan, Denmark and Peru — were introduced with the traditional red-carpet entrance and military escorts. The menu included Trump wines; the dance band (rock, not rumbas) kept the floor packed because of one other Palm Beach truism that crosses class barriers: Bless their hearts, they all love to dance.

Guests tripped out with a goody bag containing a designer candle and heavy bottle of Veuve Clicquot champagne. The party ended just in time for guests to walk past the club’s members-only bar, packed with people watching the end of the GOP debate, Trump’s face glowing from the screen.

Not actually here, but somehow omnipresent. It’s Trump’s world, and even Palm Beach has to live in it.