Mary Max, the wife of celebrated artist Peter Max, killed herself in her apartment on Manhattan's Upper West Side over the weekend.

The 52-year-old was found dead in the couple's 15th floor apartment on Riverside Drive near West 84th Street on Sunday night, according to police.

Mary, who was found dead in the apartment by a friend, died of nitrogen asphyxiation.

Her death comes amid a bitter legal battle with other members of the Max family about her 81-year-old husband's artwork and his declining health.

Peter, her husband of more than 20 years, suffers from an advanced form of dementia.

Mary Max (right), the wife of famed pop artist Peter Max (left), has died of suicide. Pictured in 2009

Mary had been embroiled in a ongoing feud with her stepson Adam Max ever since he sued her in 2015 after accusing her of attempting to kill his father so that she could take control of his multi-million dollar art collection.

In turn, Mary accused her stepson of stealing $4.3million worth of artwork that her husband had given her in a prenuptial agreement.

The artist's mental state has deteriorated significantly in recent years as the legal battles between his family have continued in court.

Mary asked a court four years ago to appoint a guardian to oversee her husband's business after Adam and three business associates took over the artist's studio.

They increased production and profit through a series of art auctions on cruise ships.

But sources told the New York Times that Peter was too ill and hadn't seriously painted for about four years.

They claimed that Peter was just signing his name to other artists work that mimicked the colorful and psychedelic style that made him such a hit with hippies in the 1960s and 1970s.

After the court granted Mary's request for a guardian, Adam removed his father from his home and moved him around New York for more than a month.

In a series of damning accusations, Mary accused Adam of concealing the whereabouts of Peter and effectively 'kidnapping' him.

Mary, 52, (right) was found dead in her apartment on Riverside Drive near West 84th Street on Sunday evening among a bitter legal battle with her stepson Adam Max, 49, about her 81-year-old husband's (left) artwork. Pictured together in 2018

She was found dead in her New York City apartment on Sunday, according to police

Peter has painted many icons and world leaders, in 2002, he presented a portrait to President Bill Clinton in New York

Berlin-born Peter (left) rose to fame in the 1960s, when he became known for his psychedelic art and pop art. He married Mary Baldwin (right) in 1997. Pictured together at the Humane Society of the United States to the Rescue Gala in 2013

Adam retorted that he was protecting his father from Mary's verbal and physical abuse, describing her as neglectful.

That view that was later supported by the guardian Mary appointed herself.

Members of household staff also accused Mary of neglecting her husband, saying she withheld food and even put 'large Brazil nuts' in his smoothies that acted as a choking hazard.

In a transcript of a recorded interview seen in court, Mary discussed with her driver about hiring a goon to intimidate her husband and to damage his painting hand.

However, one court-appointed lawyer claimed that Peter stated his love for his wife several times and that removing him from his home could have been detrimental to his well-being.

A judge ordered Peter to be returned to his wife's care at their Riverside Drive home and that a guardian oversee both his business and personal affairs.

Peter's daughter Libra, who lives in Los Angeles, took over her father's studio in January and filed a lawsuit to stop her brother from being able to interact with the company.

Mary was the famed artist's second wife.

He married Elizabeth Nance in 1963 and the pair had two children, Adam Cosmo and Libra Astro, before they divorced in 1976.

He went on to have a string of high profile relationships before meeting Mary Balkin on a Manhattan sidewalk in 1996.

Mary, a blonde with a pixie cut, caught Peter's eye. He approached her and introduced himself saying: 'I've been painting your profile my entire life.'

They married a year later and the wedding was officiated by Mayor Rudolph W. Giuliani.

Peter pictured at home in New York in 1967, before he met Mary

In a transcript of a recorded interview seen in court, Mary discusses with her driver about hiring a goon to intimidate her husband and to damage his paining hand. But Peter has said he always loved Mary. Pictured together in 2017

Peter's artwork - renowned for its colorful and psychedelic style - made him a countercultural icon.

At the height of his popularity, he was creating art for the likes of the Super Bowl, World Cup, the U.S. Open, and the White House lawn.

His works featured on everything from bed sheets to cereal boxes, to postage stamps and a chunk of the Berlin Wall.

Peter later expanded his partnership with Park West Gallery and it became a name familiar to anyone who has vacationed on a major cruise line, including Royal Caribbean, Norwegian, and Carnival.

Cruise ship auctions provide the bulk of Park West Gallery's revenue and a 'Peter Max original' is their biggest sell for customers who are willing to pay up to $30,000 for one.

His name has become so intertwined with cruise ships - who can get as much as a 40 percent cut from Park West sales - that Norwegian even has an entire Peter Max-themed ship.

The ship's hull is adorned with his Statue of Liberty.

For confidential support call the National Suicide Prevention Line on 1-800-273-8255.

Peter famously painted world leaders, including Barack Obama (pictured), and even presented art to Bill Clinton