Hedge-fund manager Glenn Dubin has recently signed a contract to buy the $32 million apartment from billionaire David Koch, according to a source familiar with the deal.

Mr. Dubin—who currently resides at nearby 1010 Fifth—is managing partner and co-founder of Highbridge Capital Management. But more interestingly, he’s also chairman of the Robin Hood Foundation, a favored charity of the late John F. Kennedy Jr., who also had a seat on its board and who grew up in the apartment Mr. Dubin is buying.

Through a spokesperson, Mr. Dubin declined to comment. And though Mr. Koch, the seller, would not identify Mr. Dubin as the buyer, he was happy to talk about the apartment he’s leaving behind.

When Mr. Koch bought the apartment back in 1995, he said, it had to be completely refurbished.

“Mrs. Onassis was very conservative financially, and she didn’t spend much on it,” said Mr. Koch. “We gutted the apartment and redid everything.”

At approximately 5,300 square feet, the 15th-floor spread includes five bedrooms and five and a half baths. There is also a library, a conservatory, a dining room, two terraces and three fireplaces.

But for the billionaire Mr. Koch—whose third child was born a week ago—that wasn’t enough space for him, his wife, three children, his mother-in-law and three nannies.

“As much as I love the old Jackie Onassis apartment, it wasn’t large enough,” said Mr. Koch.

Considering that Mr. Koch is worth an estimated $12 billion, it’s not surprising that he will be heading over to the much-celebrated 740 Park Avenue, home to fellow billionaires like Steve Schwarzman and Ronald Lauder. Purchased for $18 million two years ago, Mr. Koch’s new duplex has about twice as much space.

And he’s just completed another big renovation. Previously owned by the Japanese government, the new place hadn’t been touched in about 50 years, he said.

“Obviously, after all the money we paid for the apartment, we wanted to make sure it was first-class,” said Mr. Koch, who worked on the two-year gut renovation with renowned architect Peter Marino.

Although Mr. Koch just officially moved into 740 Park a few weeks ago, he’d already learned quite a bit about the building’s history from author Michael Gross’ biography of the storied co-op. And unlike some snooty 740 Park residents, Mr. Koch was more than happy to attend the book party: “[Mr. Gross] told me that I was the only occupant that came to cheer him on.”

So if the deal goes through, Mr. Koch—who paid $9.5 million for the Fifth Avenue apartment—could make a hefty profit (not that he really needs it).

Mr. Koch said that about 30 potential buyers passed through the apartment before they found a match. Now the couple purchasing the apartment—we say the Dubins; he won’t say anything—go before the board within the month, according to Mr. Koch.

Leighton Candler, of the Corcoran Group, has the listing. Ms. Candler confirmed that the apartment is under contract, but also would not confirm the identity of the buyer.

Ricky Martin Wants $9.95 M. at Time Warner Center

It looks like the lavish condos of the Time Warner Center are losing their most famous resident.

Latin pop star Ricky Martin has just put his 65th-floor apartment on the market for $9.95 million, according to a source with knowledge of the listing.

If all goes well, Mr. Martin could turn a nice profit, too: The heartthrob paid $6.8 million in 2004 for the apartment, according to deed-transfer records.

The nearly $10 million price tag gets you 3,000 square feet, including four bedrooms and four and a half bathrooms. (Mr. Martin’s master-bedroom suite features a marble bath.)

Of course, the floor-to-ceiling windows provide far-reaching Central Park and city views. Located in the south tower, the view should not be obscured when 15 Central Park West eventually rises nearby.

Mr. Martin leaves behind neighbors like sportscaster Bob Costas, singer Jimmy Buffett and financier David Martinez—who has dropped over $54 million for the entire 76th and 77th floors, in order to create the most expensive combined apartment in Manhattan.

Mr. Martin’s apartment is listed with Dennis Mangone, senior vice president of the Corcoran Group, and his colleague, Pablo Alfaro.

In White-Glove Condo, No Jacket Required

Singer Phil Collins has had a tumultuous spring: In March, the Grammy winner announced his split from his third wife, Orianne, to whom he’d been married since 1999; last month, the musical Tarzan—for which Mr. Collins composed the score—opened on Broadway and bombed with critics.

At the same time, Mr. Collins was dipping his toe in the Manhattan real-estate market, dropping $3.85 million on a Central Park West apartment, according to city records.

The 2,876-square-foot apartment at the Landmark, at Central Park West and 106th Street, had been listing at $3.88 million and has three bedrooms, four bathrooms, a dining room and a library.

At 106th Street, Central Park West is hardly the rarefied neighborhood it becomes 20 blocks south. But the Landmark, a full-service building created out of a former cancer hospital and a smaller, castle-like structure (complete with turrets!), commands top dollar.

The Upper West Side building is also home to Hillary Clinton’s political advisor, Howard Wolfson, who paid $1.75 million for a 1,300-square-foot pad last summer.

Mr. Collins did not return calls seeking comment.