By the time he passed away in Monaco last March, the British skyscraper developer Howard Ronson had paid $22.95 million, in three separate deals over three years, to amass a 32-room spread in the hugely ornate Berwind Mansion co-op at 828 Fifth Avenue. (Never mind that he reportedly enjoyed his later years on his yacht.)

Eleven months later, he’s posthumously added a few more rooms.

His limited liability corporation just paid $11 million, according to public deeds, for the building’s glass penthouse, which takes his family’s tally in the mansion to nearly $34 million. That number is likely to go up, considering that records show there are at least two other owners in the building to buy out, including the retired dress designer Adolfo, Nancy Reagan’s old favorite.

It’s not clear if his widow controls his real estate deals now, but two brokers said that the idea to buy the whole mansion piecemeal came from Mr. Ronson himself. Last year, two of the apartments were transferred to a children’s trust, with an address in the Channel Islands off France.

If that trust or the LLC buys up the rest of the mansion, the Ronson family will be the first to have the house to themselves since the Berwinds. The place was built 111 years ago by the mining magnate Edward Berwind, whose coal powered the U.S. Navy through World War I. He sold to his sister Julia, who sold to the Institute of Aeronautical Sciences—it was split into apartments in the 1970’s.

Even before this $11 million deal, Mr. Ronson’s units in the building included a ground-floor duplex with a 4,000-bottle brick wine cellar, a glass conservatory and a garden. Better yet, Madonna once spent 15 minutes lying face-up in the parlor floor’s oceanic gold ballroom, ogling its 18-foot ceilings. That unit’s mirrors hide routes to mezzanine bedrooms—which must have appealed to Mr. Ronson, whose New York business office was camouflaged by an oak-paneled waiting room.

The mansion overflows with flowery Napoleon-level luxury, from the painted ceilings and gold trim to the fluted columns, sculpted mantels and perfect moldings. But on the downside, the glass-paneled penthouse was rejected by Rudolph Giuliani in 2002, after three visits, reportedly because it didn’t have a separate formal dining room.

According to city records, the penthouse seller is T. Richard Butera, a developer and philanthropist, who married the sister of infamous bounty hunter Domino Harvey.

The listing is the latest chapter in the high-profile couple’s separation, which found its way into The New York Times this summer when the couple sparred over the custody of their newborn twins, which were delivered by a surrogate mother in March.

Mr. Bacon—who with his brother Louis owns a private polo field at the family’s Port of Missing Men estate in Southampton—purchased the home for $5.8 million in March 2002, city real-estate records show. The 20-foot-wide townhouse at 123 East 69th Street totals some 8,000 square feet and has six bedrooms, five bathrooms, eight wood-burning fireplaces, a wood-paneled library and a dramatic fourth-floor terrace. The historic mansion, on 69th Street between Park and Lexington avenues, was built between 1872 and 1873, and the home underwent an exterior renovation in the 1930’s. The townhouse also has unique details, even by exclusive Upper East Side standards, including an elevator, a gym with sauna and an indoor waterfall in the entrance hall.

Listing brokers Sami Hassoumi of Brown Harris Stevens and Eileen Robert of Halstead Property could not be reached for comment.

Through a spokesperson, Mr. Bacon declined to comment.

The exact origins of the couple’s fissure are not entirely known. According to previous reports, Ms. Douglas, 48, wanted to raise the children at her estate in the Santa Barbara hills, while Mr. Bacon sought to raise the children at their New York townhouse. The feud came to a head in May, when, after four years together, Ms. Douglas filed a temporary restraining order against Mr. Bacon and even had him escorted away in handcuffs by the local sheriff. According to Mr. Bacon’s spokesperson, the charges have since been dismissed, and the couple will enter into legal proceedings later this month for custody of the children.

Celebrated sitcom producer Norman Lear’s former co-op in the gilded Beaux-Arts mansion at 828 Fifth Avenue, which had once been the grand private residence of coal magnate Edward J. Berwind, is now on the market. Mr. Lear’s third-floor apartment and the fourth-floor spread above it are both available as a duplex for $10.95 million. Paula Del Nunzio, of Brown Harris Stevens, has the exclusive listing.

Combined, the duplex has 15 rooms, eight bedrooms, six full baths, two half baths, eight wood-burning fireplaces and three exposures—west, north and east. The listing is significant, as many real-estate experts attest that 828 Fifth, on the corner of the city’s most exclusive townhouse block of East 64th Street, is perhaps among Manhattan’s most storied residences.

Built in 1896 for the Berwind family—who furnished coal to the United States Navy for its fleets and to railroads up and down the East Coast, as well as for the city’s budding new I.R.T. subway system—the building was once described by architectural historian John Tauranac in The New York Times "as unabashedly Louis XV and about as close to Versailles as residential New York has to offer." When Madonna toured the second-floor apartment there—which has a grand ballroom stretching much of the building’s 110-foot length—she reportedly lay down on the floor and gazed up at the 18-foot ceilings for 15 minutes (she eventually passed on taking the apartment, as the building didn’t offer a private parking garage). Along with Mr. Lear, the building has also been home to the designer Adolfo, Cher and Institute of Aeronautical Sciences.

Berwind was a close confidante to many of the 20th century’s business titans, including Henry Clay Frick, Harvey Firestone, Andrew Carnegie and Henry Ford. Along with the grand Manhattan townhouse, the Berwinds often retreated to their Newport estate, the Elms on Bellevue Avenue, a grand mansion done in the 18th-century Parisian style.