11 Madison AvenueLois Weiss

Trophy tower 11 Madison Ave. is set to become one of biggest real estate prizes ever in the city’s history.

SL Green Realty Corp. has agreed to pay $2.6 billion for the 2.3 million square-foot Art Deco skyscraper overlooking Madison Square Park being sold by the Sapir Organization and minority partner CIM Group, The Post has learned.

That would be the biggest single-building deal in the city and the second-highest price ever paid for an office tower after the $2.8 billion sale of the GM Building in 2008. The latter was part of a $3.95 billion package that included three other towers.

The real estate investment trust, led by Chief Executive Marc Holliday and President Andrew Mathias, was set to sign a contract either Sunday night or Monday, sources said. SL Green is the city’s biggest landlord with 43.6 million square feet spanning 117 buildings.

The deal represents a victory for late developer Tamir Sapir, who died at 67 in September. Sapir bought the building from MetLife for $675 million in 2003. At the time, Madison Square Park was not deemed nearly as desirable and the city was still reeling from 9/11. CIM Group bought a stake in 2010.

Along with CIM, Sapir’s son, Alex, president of the Sapir Organization, and son-in-law and Chief Executive Officer Rotem Rosen are selling the building after tripling operating income to $120 million a year from $40 million.

“I cannot confirm anything,” Sapir said late Sunday. “This asset is the result of one man’s vision, which is my father’s legacy, and the real American dream story of taking risk, hard work and dedication in creating one of the most successful real estate stories in the history of New York.”

The other parties either could not be reached or declined to comment.

The owners faced the loss in 2017 of anchor tenant Credit Suisse, which occupied 85 percent of the building, putting its future in limbo.

In the last year, though, Sapir and Rosen, along with brokers Howard Fiddle and Brad Gerla of CBRE, worked out a new lease to take less space in the base of the building. The asking rent was in the $70s per square foot and will total around $1.8 billion over the 20-year term, sources said.

Sony followed with a 550,000 square-foot relocation, along with Yelp, the online dining reviewer, and talent agency William Morris Endeavor, all at higher rents. The last available floor is being leased for more than $100 a square foot, sources said. Restaurant 11 Madison and Fidelity Investments are two of the retail tenants.

Credit Suisse also has space and air rights at the nearby One Madison Ave., also owned by SL Green, making it the natural buyer of 11 Madison, which can host a taller tower.

Marketing was done by Darcy Stacom and Bill Shanahan at CBRE. The same pair offered it for sale a few years ago, but bidders didn’t offer top dollar because they feared a near-empty building if Credit Suisse bailed.

A handful of institutional buyers were interested in the higher pricing this time around, which worked out to $1,130 per square feet, sources said.