Hines, the developer behind the ultra-luxury condo tower rising by New York’s Museum of Modern Art, has a new project coming to midtown Manhattan: a senior-living community.

The builder, in a partnership with senior-housing owner Welltower Inc., acquired a site at the corner of 56th Street and Lexington Avenue for an undisclosed price, according to a joint statement Tuesday. They plan to tear down the existing building and construct a 15-story tower for people in need of assisted-living and memory-care services.

The site at 139 East 56th St. -- currently home to a T.G.I. Friday’s restaurant -- is in the heart of Manhattan’s office district and just a few blocks of east of the sky-piercing condominium towers of Billionaires’ Row. A senior-housing project would mark a shift for an area where ultra-luxury housing has proliferated, leading to a glut of high-end properties.

“It’s a different conversation than what we would typically have on a redevelopment site in Midtown,” said Jonathan Miller, president of New York appraisal firm Miller Samuel Inc. “The default thinking for the last five years has been that a patch of dirt is there to inevitably be a super-luxury condo tower.”

The project is the first foray into senior housing for Houston-based Hines, a global real estate developer with about $89 billion of assets under management.

Manhattan’s aging population has been “vastly underserved” in the number of assisted-living facilities available to them, Hines and Welltower said. The design and development plans for the project are under way and will be announced later, the companies said.

“Consistent with Welltower’s focus on high-quality assets in major metropolitan markets, we expect this project will support a more-connected model for health-care delivery to seniors,” Mercedes Kerr, senior vice president of business development at Toledo, Ohio-based Welltower, said in the statement.

Sellers of the site, comprising two adjacent properties, were Stephen Meringoff and Dennis Riese, according to the statement.