This Philly-made John Singer Sargent portrait resurfaced after decades — and now it’s gone again.

NEW YORK — A very Philadelphia John Singer Sargent portrait out of public view for a half-century resurfaced here Tuesday evening.

And then it quickly went back into private hands.

Sargent’s 1903 portrait of Philadelphia businessman and art collector Peter A.B. Widener was unveiled and feted at a dinner at the Explorers Club on the Upper East Side, where its sale to Blackstone Group CEO Stephen Schwarzman was announced.

The work — which captures Widener at Lynnewood Hall, the 110-room mansion he had built for himself in Elkins Park — had been in storage for decades at the Philadelphia Museum of Art.

But although it was held by the Art Museum, it was theirs on loan. The Widener family actually owned the work, and, after the Art Museum offered its return about a year ago, the Wideners sold it to Schwarzman, who in turn has made a donation toward the restoration of Lynnewood Hall.

Leaders declined to provide the sale price or the exact amount of the donation, but said the resulting gift from Schwarzman to the nonprofit Lynnewood Hall Preservation Foundation was a multi-million-dollar one.

A Philadelphia Museum of Art spokesperson said the portrait was last on display there in the 1970s. She did not answer questions about when or why it was returned to the Widener family, citing the museum’s privacy policies.

Even after Schwarzman’s gift to Lynnewood, the need at the tumbledown estate is staggering. Foundation trustees estimate the price tag for restoring the one-time Widener home at $100 million, though work would be done in stages as smaller chunks of money are raised.

» READ MORE: Preserving Lynnewood Hall: The unlikely story behind saving the Gilded Age estate in Elkins Park.

Tuesday’s event was an unlikely assemblage of a diverse cast of characters: Widener descendants now living in Wyoming who spend more time on cattle ranches than in gilded-age mansions; the 77-year-old Schwarzman, who served as chairman of the Trump administration’s Strategic and Policy Forum; Marc Rosen, a designer of perfume bottles who was the sixth (and final) husband of 1940s-’80s actress, entrepreneur, and author Arlene Dahl; and arts supporters, historic preservation buffs, and potential funders.

“While the portrait is the hook, the reason for the evening is to try to get people interested in Lynnewood Hall, in hopes of supporting the restoration,” said Rosen, a New Yorker who organized the evening and who learned of Lynnewood Hall four years ago after stumbling across photos of it on the internet.

“I never heard of Elkins Park, but knew Philadelphia, and I became obsessed,” Rosen said.

Schwarzman, whose net worth is estimated to be north of $40 billion, has more than a passing interest in Lynnewood Hall, Sargent, and Widener. He graduated from nearby Abington Senior High School and in 2018 pledged a controversial $25 million gift to the school, though he said Tuesday that he wasn’t familiar with Lynnewood Hall when he was growing up.

“Never even heard of it. It’s ironic,” Schwarzman said, given that he’s recently acquired Miramar, in Newport, R.I. which, like Lynnewood Hall, was designed for the Wideners by Philadelphia architect Horace Trumbauer. It will now be the home of Schwarzman’s newly acquired portrait.

“It was sort of an impulse buy,” Schwarzman told the dinner crowd of about 80 of his $27 million acquisition of Miramar.

The Newport mansion was commissioned by George Dunton Widener, Peter A.B. Widener’s son. He never got to live in it. George Dunton Widener and his son Harry died in the sinking of the Titanic in 1912.

But the Widener family is once again engaged in their ancestral home in Elkins Park. Peter A.B. Widener’s great-great-great-grandson, Peter R. Widener, is now chairman of the Lynnewood Hall Preservation Foundation board.

“Lynnewood is one of those places that just consumes you,” said Widener. “It takes days just to see.”

The Widener scion, who is 40, envisions a future for Lynnewood Hall as an “incubator” for education in the arts, historic preservation, architecture, horticulture, and more. “I’d love to see the surrounding area benefit,” Widener said. “I’d love to see Michelin chefs trained there. Maybe a charter school.”

“We’re not just filling it with antiques — buy a ticket, take a tour,” says Edward Thome, CEO and executive director of Lynnewood Hall Preservation Foundation. “But it’s going to be educational. It’s a really great thing for Philadelphia.”

Of the Sargent portrait of his Philadelphia ancestor, Widener said: “It wasn’t going to fit in any of our homes.”

Plus, he had visions of his three young sons throwing Legos at the nearly life-size work with elaborate gilded frame, he joked.

Sargent, who died in 1925, completed around 900 oil paintings, many of them portraits. His most famous was perhaps Madame X.

Another Sargent portrait of Widener is in the collection of the National Gallery of Art in Washington, which was gifted nearly 2,000 works from the Wideners in 1942. But Widener posed for that portrait a year earlier than Schwarzman’s new acquisition, in London, and it shows its subject against nothing more than a paneled wood door.

The work from Lynnewood Hall, in contrast, portrays Widener in his own home, with considerably more context and complexity.

“It has an interesting and special quality that you see in Sargent’s great portraits,” said Stephanie L. Herdrich, associate curator of American painting and drawing at the Metropolitan Museum of Art.

Herdrich — a Sargent specialist who spoke at Tuesday’s event but played no part in the sale of the painting — said the first Sargent portrait of Widener “feels very traditional to me, and then thinking of the [second] painting just a year later there’s much more liberty and experimentation.”

By the time Sargent did the second portrait, he knew Widener and his family better. He painted it while staying with them at Lynnewood Hall.

“I think that what’s extra interesting is that it shows him at Lynnewood Hall with an Old Master painting behind him, speaking to his activity as a collector, his sophistication, and his taste as a collector, but also creating a pretty interesting composition,” said Herdrich.

(The background painting-within-a-painting, The Satyr and the Peasant, a scene from Aesop’s Fables, was once thought to be by Velazquez, but is now attributed to 17th century German painter Johann Liss).

Sargent’s 1903 portrait of Widener may now live at Miramar, in a private home. But Schwarzman told Tuesday’s crowd that he considers himself a “custodian of history,” and after his death he intends for the house to be opened up as a museum. Which means the portrait would then be on public display once again.

“I couldn’t be prouder to have this picture,” said Schwarzman. “It’s a big deal. It’s a big deal to me.”