The Metropolitan Museum of Art, the largest art museum in the United States, and one of the largest of its kind in the world, announced this week that it had received a collection of Cubist works valued at roughly $1.1 billion from noted art collector, philanthropist, and cosmetics heir Leonard Lauder.

Thomas Campbell, director and CEO of the Manhattan-based museum, called Lauder’s donation of 78 drawings, paintings, and sculptures a “transformative” gift to the museum that would change the course of its 143-year history.

Lauder, chairman emeritus of The Estée Lauder Companies, turned to Simpson Thacher & Bartlett for counsel on his deal with the Met, which The New York Times reported this week was in the works for several years before finally being approved Tuesday by Lauder and the museum’s board of trustees. (Forbes notes that Lauder, who is worth about $8.1 billion, is effectively ceding 13.5 percent of his net worth to the Met as a result of the deal.)

A team of lawyers from Simpson’s exempt organizations practice—led by personal planning department partner Laura Twomey, counsel Jennifer Franklin, and associates Gena Hatcher and Maura Whelan—worked on the matter, according to a press release issued by the firm.

While neither Twomey nor Franklin responded to requests for comment, Simpson has long-standing ties to Lauder. A 2011 tax filing by the New York–based foundation established by Lauder and his late wife Evelyn—which operates out of the same building as Estée Lauder’s global headquarters—shows that Simpson was paid $7,442 for unspecified legal services. (Pillsbury Winthrop Shaw Pittman received $4,594 from Lauder’s foundation, of which Joel Ehrenkranz of New York’s Ehrenkranz & Ehrenkranz is a director.)

A former Simpson associate, Lynn Forester De Rothschild, is an independent member of the board of directors at Estée Lauder. Rothschild, who currently serves as CEO of her own private investment firm, joined Estée Lauder’s board in 2000.

Other independent members of Estée Lauder’s board include Wilmer Cutler Pickering Hale and Dorr senior international partner Charlene Barshefsky and former Orrick, Herrington & Sutcliffe lawyer Wei Sun Christianson. Richard Parsons, a former managing partner of New York’s Patterson Belknap Webb & Tyler and ex-chairman of financial services giant Citigroup, is also a director for Estée Lauder, whose general counsel is Sara Moss.

Simpson also has close ties to the Met. In 2009 the firm cohosted a breakfast at the museum for 112 high-powered women lawyers and executives, according to our previous reports. Simpson held the same forum again at the Met in 2011.

Conrad Harper, a retired Simpson partner and former president of the New York City Bar Association, was elected in 1996 to serve on the Met’s board of trustees. The Met itself is governed by 41 elected trustees, several of whom besides Harper are prominent attorneys—such as Hughes Hubbard & Reed chair Candace Beinecke, attorney-turned-private-equity-investor Jeffrey Greenberg, and James Ross of former New York firm Becker Ross & Stone. (Another longtime trustee, former Kramer Levin Naftalis & Frankel real estate partner Samuel “Sandy” Lindenbaum, died last year.)

Sharon Cott, the Met’s general counsel since 1999, did not respond to a request for comment about the deal with Lauder or whether the museum retained its own outside counsel for its negotiations to acquire his Cubist collection. (The Times has assembled its own interactive tour of the pieces being donated by Lauder.)

The Met, a registered nonprofit, disclosed in annual tax filings with the IRS that Cott’s annual compensation was $439,407 for fiscal year 2010, the most recent year for which records are available.

Lobbying records on file with the U.S. Senate show that the Met paid $60,000 in 2012 to Todd Howe, president of WOH Government Solutions LLC, a Washington, D.C.–based subsidiary of Albany’s Whiteman Osterman & Hanna, to advise the nonprofit before Congress and other federal government institutions.

The Met, of course, also occasionally has the need for other types of counsel.

Last month Arnold & Porter litigation partners Anthony Boccanfuso and Bruce Kelly and senior counsel Michael Gerrard filed a 20-page response to a suit slapped against the museum in New York State Supreme Court in November 2012 over the Met’s “recommended” $25 entry free. Plaintiffs in the case—led by one New York resident and two tourists from the Czech Republic—are being advised by Michael Hiller of New York’s Weiss & Hiller.

It was not immediately clear Thursday what potential tax breaks, if any, Lauder himself could reap as a result of his monumental donation to the Met. The Times reported in 2011 on his billionaire brother Ronald Lauder’s use of art purchases and donations as a carefully crafted tax strategy. Simpson is a longtime legal adviser to Ron Lauder and his various corporate entities.