When John Mack, then the chairman and CEO of Morgan Stanley, and his wife, Christy Mack, decided to return to Manhattan after raising their three children in suburban Westchester County, Christy had one condition: she wanted a turn-key townhouse.

"We moved to Westchester when my youngest was 6 months old," said Christy, a philanthropist. "I said, 'I can't do an apartment again.'"

But after an exhaustive and fruitless search for a townhouse that met their needs, the Macks discovered a diamond in the rough: a brick-and-limestone carriage house on the Upper East Side with its original stables intact.

"I wanted turnkey, but my daughter showed me this house -- it was a total gut -- and said, 'Mom, you have to buy this. It has great energy in it,'" said Christy. "So we did." They paid $13.5 million in 2009, according to public records.

The complex renovation that followed would delay the family's move by six years. The spartan stables gave way to a lavish, 20-room residence that stretches six floors, from cellar to solarium.

Now, after more than a decade at the home, the Macks have left the city once again. John stepped down as chairman of Morgan Stanely in 2011, and the Macks are retiring to their home state of North Carolina.

They are listing the converted carriage house for $80 million, making it the priciest townhouse on the market in New York City. If the six-bedroom home fetches its asking price, the sale would set a city record for a residential townhouse, according to appraiser Jonathan Miller of Miller Samuel.

The roughly 16,000-square-foot carriage house was built around 1902 by the celebrated Gilded Age architect C.P.H. Gilbert for banker Henri P. Wertheim, who lived nearby. The then-four-story building was later owned by a Who's Who of wealthy New Yorkers, including Otto Kahn, the builder of Oheka Castle on Long Island; Singer sewing machine heir Stephen Carlton Clark, who founded the Baseball Hall of Fame, and Rachel Lambert "Bunny" Mellon, the widow of banking heir and horse breeder Paul Mellon.

As automobiles replaced carriages on the streets of Manhattan, a portion of the gabled structure was converted into a garage. It was still being used as a garage when the Macks bought the property from Mellon, and was one of the last carriage houses remaining in the neighborhood with its original stables, according to listing agent Mike Fabbri of the Agency.

"It still had the horse ramps and stalls, like a barn," said Christy. "When we bought it, there was nothing but cars in it. I thought, 'What in the world are we going to do with this space?'"

To oversee the top-to-bottom overhaul, the Macks hired New York architect Sawyer Berson and interior designer Eleanor B. LaSota.

Wherever possible the team preserved historic details. Chicken-wire transom windows were incorporated into the mudroom doors. Crackled tiles were sorted by artisans and arranged on the walls of the gym. Hoof-scraped wooden ramps were discovered to be thick virgin chestnut and reused as wainscoting. At the same time, contemporary comforts were added, including a wine cellar, a home theater, a gym and a spa suite with a massage room and hot tub.

Since the home was originally designed for four-legged occupants, the proportions are larger than many New York townhouses, said Fabbri, noting that the living room is about 31 feet wide. That outsize scale is reflected in the asking price, Fabbri said.

The previous record was set in 2019 by a townhouse sold by hedge-fund manager Philip Falcone; it closed for $77.1 million.