Warren Buffett, the ninth-richest person in the world, appears to be taking steps to distance himself from his embattled billionaire friend Bill Gates, resigning from his position as a trustee of the Bill and Melinda Gates Foundation after 15 years in that role.

Buffett’s departure, announced on Wednesday, comes as the foundation is embroiled in multiple scandals, including allegations of misconduct toward women—directed at both Bill Gates and the money manager of the Gates Foundation’s endowment, Michael Larson. Both men deny the allegations.

The timing of his resignation also comes shortly after Buffett himself was the subject of a ProPublica investigation into how little income tax billionaires pay, which reported Buffett’s “true tax rate” as only one-tenth of 1 percent between 2014 and 2018.

These recent controversies are especially notable for the 90-year-old Buffett—who has largely avoided close scrutiny through decades of work as a high-profile investor and public figure. Buffett’s widely cited financial advice often doubles as a kind of grandfatherly wisdom—”Opportunities come infrequently. When it rains gold, put out the bucket, not the thimble”—and has helped earn him the nickname “the Oracle of Omaha.”

His resignation from the Gates Foundation’s board appeared almost as a footnote in a lengthy public letter he published earlier this week reflecting on his years of philanthropic giving. While Buffett offers no acknowledgement of the misconduct allegations surrounding the foundation, buried in the letter is an assertion that his “goals are 100% in sync with those of the foundation.”

Yet tax experts note that Buffett may not have much choice in the matter. He appears to be legally obligated to continue giving billions of dollars to the foundation.

In 2006, Buffett dispatched a letter to Bill and Melinda French Gates stating that he was “irrevocably committing to make annual gifts of Berkshire Hathaway ‘B’ shares throughout my lifetime.” That letter even specifies that if he were to become “incapacitated…and be unable to administer [his] affairs,” he would continue to make yearly contributions of Berkshire Hathaway stock to the foundation. Buffett also noted that he intended to ensure through his will that his giving would continue after his death.

Ohio State University accounting professor Brian Mittendorf directed The Nation to the letter, and also pointed to financial audits of the Gates Foundation that confirm Buffett’s commitment, described as conditional on three seemingly minor requirements, including that Bill or Melinda French Gates must remain active at the foundation.

Inside the Gates Foundation, CEO Mark Suzman put a happy face on Buffett’s resignation, publishing a statement that his departure came with a new $3.2 billion donation—his largest ever to the foundation and a signal of his continuing support. But Buffett’s large donation is simply the result of Berkshire’s rising stock price. (His yearly donations of stock to the foundation proceed according to a formula he devised in 2006, and have trended up in value with Berkshire’s share price.)

According to the foundation’s most recent financial audit, Buffett has only given the foundation slightly over half of the Berkshire shares he committed in 2006. The remaining committed shares, scheduled to be donated on a yearly basis, are currently valued at more than $60 billion. This schedule, however, does not appear capable of delivering all his committed shares before his death, and it is not clear what Buffett’s will stipulates about donations after his death. Press inquiries sent to the Gates Foundation and to Buffett (through Berkshire Hathaway) were not answered.

While Buffett describes his resignation as merely a consequence of his getting older and retiring from professional responsibilities, it coincides with the continuing controversies emerging around Bill Gates. The same day as Buffett’s announcement, new questions surfaced around the Gates Foundation’s money manager, Michael Larson, who also manages much of Bill Gates’s private wealth.

A letter from the International Brotherhood of Teamsters to Republic Services, the second-largest sanitation company in the United States, called on the company to ask Larson to resign from the board of directors of Republic, in which Gates has a 34 percent personal ownership stake. The letter argued that the “the high-profile allegations against Mr. Larson, which include bullying, sexual harassment and racist comments,” threaten to “erode investor confidence in the board as a whole.”

The Teamsters hold a financial stake in Republic, but the union also exerts influence on the sanitation giant because its members make up 20 percent of the company’s workforce. The Teamsters have long highlighted the outsize financial benefits Bill Gates receives from his investments in Republic, and pushed the company to redirect corporate profits into worker pay.

The union’s letter to Republic cites reporting by The New York Times that revealed that Bill and Melinda French Gates put Larson on paid leave during an investigation of one allegation against him of misconduct. That investigation did not substantiate the underlying complaint.

But while Larson was on paid leave, the Teamsters note in the letter, he appears to have continued to serve on Republic’s board. The union asked Republic’s board chairman, Manuel Kadre, to explain why this was. Republic did not respond to questions sent by The Nation.

The Teamsters’ letter could have impacts that resonate far beyond Republic, prompting scrutiny of other corporate appointments Larson holds, including serving as a director of EcoLab, a water treatment company in which Gates owns a significant stakes.

In the letter announcing his departure from the foundation, Buffett mildly reproaches himself for having practiced philanthropy as a kind of absent father—writing checks instead of engaging in hands-on work, like tutoring children or aiding the elderly. He also describes himself as having been an “inactive trustee” of the Gates Foundation.

Georgetown law professor Brian Galle notes that in Washington state, where the Gates Foundation is headquartered, the law stipulates that board members at private foundations “have a duty of care. You actually have to pay attention to the foundation.”

Galle says that if the state attorney general were to take an interest in the allegations of misconduct surrounding the Gates Foundation and find it is not being competently managed by attentive board members, the state could take steps to replace the current board.

Many observers say the foundation should have long ago recognized the need for a larger and more diverse leadership. With Buffett’s departure, Bill and Melinda French Gates are the only remaining members of the board of trustees.

“In the short run…whatever [management] problems there were, they are more pronounced,” observes Brian Mittendorf from Ohio State. “Now there are just two people at the top, and those people are going through divorce proceedings. Again, this is a $50 billion organization. You would expect more stability at the top.”

The foundation has already hinted at the possibility of creating a new board, and Galle says Buffett’s exodus should expedite management changes—and may foreclose on any potential scrutiny by the Washington attorney general.

“It looks likely—and this also goes to one other reason why Buffett might have done what he did—without him there, there has to be a restructuring of that board. I think that’s coming,” said Galle. “And maybe the attorney general just wants to see what will happen.”

In response to press inquiries, the attorney general’s office said only, “Our office has a policy of generally not commenting on pending investigations, including confirming whether or not they exist.”

Buffett’s letter also includes a revealing, if contradictory, note about his personal taxes, which downplays the benefits he has received from his charitable donations, noting that “philanthropic contributions can generate significant tax deductions for the donor. That benefit, however, is far from automatic” [emphasis in the original].

He goes on to argue that he receives only 40 cents in tax benefit for every $1,000 he gives away—an arithmetic that doesn’t add up, according to tax experts.

“The actual tax benefits are likely much greater,” notes Ray Madoff, law professor at Boston College, noting that Buffett’s donations avoid both capital gains and estate taxes.

If Buffett were to cash in his Berkshire Hathaway stock instead of donating it to the Gates Foundation, Madoff notes, he would pay a 20 percent tax on the increased value of the stock. In addition to avoiding this capital gains tax, his donations “avoid gift and estate taxes which would otherwise be imposed at a 40 percent rate. In addition, it is likely that he has received at least some—even if limited—benefits from the ability to offset his ordinary income.”

“At a minimum he is saving $400 [on every $1,000 he donates], but it could be as high as $740,” said Madoff.