The widow of billionaire industrialist David Koch has sold the couple’s Manhattan’s Upper East Side mansion for a staggering $41 million to an unknown buyer in an off-market deal.

Philanthropist Julia Koch, 61, listed the East 76th Street townhouse on the market last year for $48 million, after her husband David died from prostate cancer in August 2019 at the age of 79.

The buyer of the lux property was not revealed, but a spokesperson told The Wall Street Journal that Julia and her family are committed to staying in New York – though she would not provide further details about the mega deal.

The Kochs had originally bought the 15,000 square-foot property in 2018 for $40.2 million from real estate magnate Joseph Cherit, whose original asking price was $51 million, according to The Real Deal.

David and Julia – who was ranked the second richest woman in the world with a fortune of $59 billion in Forbes’ ranking in April – originally paid for the home in cash, The New York Post had previously reported.

Couple: Julia, 61, and David Koch, 79, pictured. Julia Koch became a widow in 2019 after her husband and billionaire industrialist died from prostate cancer

The philanthropist widow listed the Upper East Side townhouse on the market last year and was recently sold to an unknown buyer for $41 million in an off-market deal

The luxury Park Avenue property renovated by architect Peter Marino boasts eight bedrooms, a grand open staircase connecting six stories and a garden.

The home also features a spa, walkout sports court and custom media room, records show.

Additional properties Julia owns includes two Upper East Side apartments she purchased in 2022 from the estate of Microsoft co-founder Paul Allen for a total of $101 million.

In late 2021, she also doled out $70 million for an oceanfront estate in Southampton, records show. She also has a home in Palm Beach, Florida.

And the Kochs’ apartment in the exclusive 740 Park Avenue building is also up for sale with Corcoran Group for $48million.

‘Every detail of the 76th Street townhouse was perfect, and we are now excited to focus on the sale of Mrs. Koch’s recently renovated 740 Park Avenue apartment,’ Leighton Candler, Koch’s broker for East 76th Street and the 740 Park Avenue co-op, told the Wall Street Journal.

The 740 Park Avenue address has been dubbed ‘the world’s richest apartment building.’

Residents have included Thelma Chrysler Foy, heiress to the Chrysler fortune, bridal designer Vera Wang and fraudster Bernie Madoff.

In 2006, the book ‘740 Park: The Story of the World’s Richest Apartment Building’ was published by author Michael Gross on the opulent dwelling, exposed some of the horrors many of its billionaire residents had to endure.

Some of the disasters included a heist where $250,000 jewelry was stolen, flooded apartments plagued by poor plumbing, and a fire that tore through the building.

Leighton Candler of the Corcoran Group, who represented Julia Koch in the latest sale is also the listing broker for Julia Koch’s co-op at 740 Park Avenue that is priced around $48 million

Pictured: 740 Park Avenue where Julia Koch has an exclusive apartment on sale for $48million

David Koch purchased the co-op at 740 Park Avenue from the Japanese government for about $18 million in 2004 out-biddng fellow billionaire Leonard Blavatnik, as per The Real Deal.

David Koch, a chemical engineer and businessman, joined the family business, Koch Industries in 1970 that would later lead to his staggering fortune.

David, who was also known as a political activist, along with his brother Charles Koch used their wealth to back conservative political causes and candidates.

The Kansas-based company would became the second largest privately held company in the United States. David Koch served as an executive president until his retirement in 2018 that was due in part, to his ailing health.

Julia Koch serves as president of the David H. Koch Foundation. The nonprofit’s mission is committed to advancing the philanthropic legacy of her husband to enrich the lives of individuals around the world through science and medical research, education, public policy, and the arts, as per their website.