It’s an art-world family feud as a nephew of legendary artist Helen Frankenthaler is accusing relatives of “grabstract expressionism” in a new lawsuit that also slams one cousin’s work as “unremarkable.”

The directors of a $1 billion foundation meant to promote the artist’s work are engaging in “pay to play” transactions to pump up their own work — and “destroying” the abstract expressionist’s legacy as one of the most important American painters of the last century, according to the lawsuit, filed Wednesday in New York State Supreme Court.

The feud finds Frankenthaler’s nephew Frederick Iseman — an ousted board member of the Helen Frankenthaler Foundation Inc. — suing his artist cousin Clifford Ross, as well as Lise Motherwell, who is the late painter’s step-daughter.

Both are on the board.

“They have been acting as if they are members of some small, private clique, using their roles as directors of the board of the foundation to promote their own careers and prestige, not to mention trading foundation assets for their personal benefit,” the court documents say.

In a clever twist, the lawsuit accuses the plaintiffs of “engaging in a kind of ‘grabstract expressionism’ that is effectively destroying Frankenthaler’s legacy.”

It also claims that Iseman, 71, was removed from the board by other members who “secretly schemed” to get rid of him earlier this year.

Michael Hecht, a New York-based accountant and board member, is named as a defendant but is not a family member.

A representative for the Helen Frankenthaler Foundation had no comment.

The lawsuit refers to Ross’ “struggling artistic career” and notes that while he “may have experienced a measure of success at some point in his career … those days have long since passed.”

The suit does not hold back in its portrayal of Ross, 71, who is the board’s president.

It alleges that the professional artist, and son of Frankenthaler’s middle sister, Gloria, engaged in “pay to play” transactions for his own benefit — and disses his talent.

Ross allegedly traded $1.8 million in foundation grants between 2013 and 2021 in exchange for exhibitions of his “own otherwise unremarkable artwork and to generate publicity for his own career,” court documents say.

The suit accuses Ross of “self-dealing” and using the foundation’s influence and funds to get his own work seen —providing “him with a platform from which he cannot promote himself,” the court filing says. It alleges that he used foundation funds to make donations to small non-profit magazines, such as Bomb and Brooklyn Rail, in exchange for promoting his work in their articles.

In 2021, the foundation donated $75,000 to the National Gallery of Art in Washington, DC, where Frankenthaler’s seminal painting “Mountains and Seas” is on long-term loan.

A year later, Ross offered to donate one of his own works to the gallery for its permanent collection, which the gallery accepted but did not place on public view.

Once the gift was accepted, the legal papers say, he promoted himself even more: directing the foundation to update his biography on its website to acknowledge that his work was in the National Gallery’s collection, according to legal papers.

According to the lawsuit, once Ross took over as president from Iseman, he “even had the chutzpah” to “immediately” update his own Wikipedia page to reflect it, under the pseudonym Brooklynartlover.

For his part, Hecht engaged two of his own accounting firms to do work for the foundation — a conflict of interest for board members, the lawsuit says.

“Hecht never sought an external audit of the foundation’s financials, despite the foundation’s high net worth,” the lawsuit says.

He also used foundation cash to donate to institutions where he serves as a board member — including, the lawsuit alleges, $5 million to liberal arts college Bennington College in Vermont where Frankenthaler went to school and where Hecht is a trustee.

Motherwell, 68, who has been president of the board of the Provincetown Art Association and Museum (PAAM) in Provincetown, Mass., since 2017 — “a position she got because of her last name, familial connections and her position on the board of the foundation” — used her influence as a board member to curate a show of Frankenthaler’s works in 2018 at the small museum, despite having no curatorial experience, the lawsuit says.

It adds that she also convinced the foundation board to donate five Frankenthaler watercolors worth $1.4 million to the museum.

“The donation furthered her reputation and cemented PAAM’s debt to her,” the lawsuit says, adding that Motherwell also asked the foundation pay her $180 per hour for her work on the board.

Frankenthaler, who died in 2011, started the eponymous foundation in 1984 to safeguard her legacy and promote her work around the world, according to the nonprofit’s mission statement.

According to the court papers, she personally named Iseman, a philanthropist and founder of private equity firm CI Capital Partners, to the board of directors.

Iseman had “a uniquely close relationship” with his aunt “and served on the board with no financial interests” until his dismissal, according to the lawsuit.

Born in 1928, Frankenthaler’s artistic genius was noted at a young age when, at nine years old, she won an honorable mention in a drawing contest sponsored by Saks Fifth Avenue.

Following her graduation from Bennington, she returned to New York and began her artistic career influenced by contemporary artist Jackson Pollock, among others.

She married artist Robert Motherwell in 1958 but divorced him in 1971.

The foundation is the primary beneficiary of Frankenthaler’s work, according to her 2004 will, court documents say.

Some of the artist’s work, which has sold for millions of dollars and is featured at the Museum of Modern Art and other important venues around the world, will be auctioned this week by Christie’s in New York.

Those works are not owned by the foundation, according to the auction house’s catalogue, which has set estimates as high as $1 million.