New York’s most secret, and storied, mansion has been put up for sale for the first time in decades — and luxury real estate agents can’t wait to see it.

In May, Dame Jillian Sackler, widow to the Purdue Pharma kingpin Arthur Sackler died at age 84 from esophageal cancer.

Since the 1980s, Sackler had been the primary resident of the devilish address 666 Park Ave., a triplex “maisonette” at the base of the 660 Park Ave. co-op tower, which stands at East 67th Street. She shared it with her late husband, who died in 1987.

Now this one-of-a-kind dwelling could head into a new generation of ownership.

Dame Jillian Sackler passed away in June. She was the widow of Arthur Sackler, who died in the 1980s — and was a member of the now-disgraced Purdue Pharma family. The Washington Post via Getty Images

The maisonette has its own entry, seen at left. Olga Ginzburg for N.Y. Post

In case your family name doesn’t grace a wing at the Met, here’s a little catching up: A maisonette is the stuffed pheasant of rarefied Manhattan real estate — a townhouse-like residence within a larger building, usually on the ground floor with a separate entrance.

Spot their inconspicuous front doors — easily mistaken for the entries to doctors’ offices — around Beekman and Sutton places or Fifth and Park avenues.

Rarified aerie

Though traditionally bearing the No. 666 mark, it appears the address has changed recently to blend in with the existing No. 660 edifice, with the address 660M.

Address aside, this perch is nonpareil even within the competitive, money-no-object milieu of Upper East Side roosts.

“Surely,” the New York Times gushed in 1981, it’s “the greatest maisonette ever constructed in New York.”

Not only is it massive — it occupies the complete second, third and fourth floors (each roughly 4,000 square feet) in the 14-story, 12-residence building — it’s decked out like an English country seat.

It’s the kind of serious house where a 50-foot long, 24-foot-high drawing room dressed with 18th-century pine paneling excised from the old Spetisbury House manor in Dorset sits comfortably.

There are between 21 and 27 rooms in total that have served as vessels for early 17th-century French Chinoiserie from the Château de Courcelles in northwestern France, sections of Georgian paneling pinched from a house on Grosvenor Street in London — as well as Sackler’s bowerbird hoard of antiques.

Arthur collected Renaissance majolica, Shang dynasty oracle bones, Post-Impressionist paintings and whatever else he could get his hands on.

Elsewhere, Corinthian columns frame a large window, a grand oval staircase slithers past a mezzanine, ornate chimney pieces radiate warmth and a wonderfully obsolete “card room” receives guests.

At the time it was built, plans called for 10 servants’ rooms. 

The building bore the addresses 660 and 666, as seen in this archival image. Google Maps

 ‘Private’ equity

“If you include the entrance and its small foyer and stairway, it’s actually a quadruplex apartment,” said Andrew Alpern, who has visited the splendid spread and featured it in his 1992 book “Luxury Apartment Houses of Manhattan.”

If all that seems offensively old fashioned for a building built in 1927 at the height of the Jazz Age, that’s the point. Its developer Frederick Ecker, a captain of Metropolitan Life Insurance, tapped staid and conservative architects York & Sawyer to conceive the limestone facade — a firm best known for institutions like banks, clubs and colleges, not to mention the New York Historical Society.

It would be erected in opposition to the emerging Chrysler Building-modernism that was coating the city in chrome.

It wasn’t alone in its rigid traditionalism, but in a city that never sits still, where homes are expected to be updated with the latest fashions — and where developers dice up historic charmers like mad vivisectionists — No. 666 somehow survives much as it always has.

“I cannot imagine that Sackler made changes of any significance to the main rooms,” added Alpern. “I suspect that he threw together some of the maids’ rooms — there were a ton of maids’ rooms and only a couple of guest rooms. I’m sure he updated the kitchen and the bathrooms and air conditioned the place, and probably put in new electricity.

But other than that, I would bet that the place probably looks very, very similar to the way it looked when it was first built.”

Alpern suspects all that because only a few privileged visitors have seen inside the home in recent decades. Moreover, it has only had four owners in nearly 100 years.

Those who have toured inside include Imelda Marcos in the early 1980s (she bought the contents of the home at that time), and more recently singers Luciano Pavarotti and Placido Domingo. The home is otherwise a closed book. Its most recent photos come from a 2002 Architectural Digest feature.

The interior of the Vanderbilts’ former Fifth Avenue mansion. Library of Congress

The exterior of that former dwelling, which stood on 52nd Street and Fifth Avenue. NYPL Digital Collections

Splitting assets

As for its slightly satanic sounding address, thank turn-of-the-century socialite Virginia Fair Vanderbilt for that. Newly unwed from playboy hubby William K. Vanderbilt II, she ditched the family nest, a Stanford White-designed palace at 666 Fifth Ave., to custom-design the maisonette at 660, for which she paid a then-record-setting $185,000 in 1926.

Insisting on a separate address, she christened it No. 666, a reference to her former Fifth Avenue digs.

It was a brash exercise in real estate one upmanship — and perhaps spite.

Not long before, Vanderbilt’s ex-husband had moved into another maisonette across the street at 655 Park Ave. Hers was better. Hers was bigger. Trump card played, and she never moved in. Instead, she fled further uptown where she commissioned a new standalone mansion at 60 E. 93rd St., which last traded hands in 2022 for $52.5 million.

Prohibition Era booze business behemoth Seton Porter picked up the pieces. He purchased No. 666 and completed the construction, creating much of what can still be seen today.

The maisonette alone takes up three floors of the co-op building. Olga Ginzburg for N.Y. Post

The co-op saw its most recent sale in 2022 — and it was in the millions of dollars. Olga Ginzburg for N.Y. Post

Turning a page on Park Avenue

But now, many years on, could this kind of residence find its next owner?

Corcoran broker Kane Manera said that maisonettes are a unique niche of New York’s upscale real estate environment and attract an equally niche buyer. Like townhouses, he said, they typically trade at a lower price per square foot compared to upper-floor apartments.

The most recent sale in the building was back in 2022, when billionaire heiress Aerin Lauder sold her 11th-floor spread to a Goldman Sachs exec for $19.5 million.

Despite being roughly three times larger, Manera doesn’t think that you can simply triple that price for the Sackler’s shack.

“People want a view. They want light. They want privacy,” he said. “Some people don’t feel secure with their door directly on the street in New York. Other people are completely fine with it.”

There are other obstacles, too. The building is ruled by a tough board, insiders said, that will put any potential buyer through the wringer. The co-op also requires deals to be made in cash, with multiples of the sale price held in liquid reserves.

“The weakest segment of the luxury market is high-end Park, Fifth and Central Park West co-ops,” said real-estate appraiser Jonathan Miller, of Miller Samuel. “The condo invasion has crushed the co-op. In fact, over the last decade, values for high-end co-ops are lower. The problem is that difficult co-op boards are devaluing these places by being a barrier to entry. The other thing is that the new condo product is tall and generally narrower. So they have 360-degree views.”

The cost of living history

Then there is the small matter of its splendiferous anachronistic outfitting. A buyer who wants to take on the preservation, or reinvention, of a home this dated, on this scale, may be one in a million. Still experts guess that a ballpark of $40 million, give or take, sounds about right without having seen it.

“So long as the interior is not landmarked, as long as you and your designer can take the best of what’s there and incorporate that into something more livable and modern that doesn’t feel like an interior at Harvard University, you have exciting potential,” Manera said.

The building is known for its handsome limestone facade. Olga Ginzburg for N.Y. Post

A world of opulence is known to live within the maisonette’s walls. Olga Ginzburg for N.Y. Post

Finally, there’s the question of the previous owners. 

In June, there was a $7.4 billion judgment against the Sackler family and Purdue Pharma for peddling opioids. Roughly $6.5 billion of those funds will come from the family’s personal fortunes.

However, Arthur purchased No. 666 and died years before the company started its OxyContin campaign; Jillian isn’t specifically named in the settlement. The couple produced no children and it’s currently unclear who will inherit the home, or if it will get tied up in the settlement, details or which have yet to be released.

“He died over 30 years ago, and he’s the scapegoat,’’ Jillian told the Washington Post in 2019 in defense of her late husband’s legacy. “It’s absolutely incredible.’’

Regardless, Miller thinks that for the right cloven-footed billionaire, this could be a once-in-a-lifetime opportunity to raise a little hell.

“If I were a wealthy enough person to buy something like this, just the fact that it was No. 666 would appeal to me as an FU to society.” he says. “That’s pretty cool.”