Ajit Jain has been a feature at Warren Buffett’s side since he left McKinsey & Co. to join Berkshire Hathaway in 1986, helping to grow the conglomerate’s suite of insurance businesses into a global powerhouse over the years. But now Berkshire’s 73-year-old vice chairman of non-insurance operations is selling stock.

Jain sold 200 Berkshire Class A shares on Monday for roughly $139 million, representing roughly 55% of his total stake in the conglomerate. He now holds just 61 Berkshire shares personally, as well as 55 shares in a family trust, and 50 in a nonprofit corporation called the Jain Foundation. Buffett has famously never split Berkshire’s Class A stock, which discourages short-sellers and high-frequency traders, and is meant to encourage long-term value investors. Jain sold his shares at an average price of $695,417.65 per share. At that price, the value of his remaining stake is about $115.4 million.

What motivated Jain to sell is still unclear, but it could simply be a matter of taking profits at an opportune time. “I’d say it’s a bit surprising,” Steve Check, president and CIO of Check Capital Management, which has 24.4% of its holdings in Berkshire Hathaway, told Fortune of the move. “The only reason I can come up with for why he is selling is he thinks the stock is fully priced, and it is—it’s probably as fully priced as it’s been since before the financial crisis, trading at something like 1.65 times book value.”

Jain certainly took advantage of Berkshire’s booming share price with his recent sale. Berkshire stock has soared nearly 23% year to date, pushing the megaconglomerate’s market capitalization above the $1 trillion mark for the first time in its history. That’s compared to a roughly 17% rise for the S&P 500 over the same period.

Tax considerations could also be behind Jain’s sale. “If he thinks that capital gains tax rates are going up in the future, he may want to take advantage of, let’s say, the relatively low rates today,” Check argued.

After the latest presidential debate, many national polls shifted in the direction of vice president Kamala Harris, who plans to raise the top capital gains rate from 20% to 28% if she’s elected. Jain could simply be taking profits before those policies go through.

Berkshire shareholders like Check aren’t worried that Jain’s sales are a sign that the stock is overvalued, or even that the veteran manager will soon retire, although Jain’s retirement has been a topic of discussion at recent shareholder meetings.

If Jain were to retire, it certainly would be a big blow for Berkshire. The Indian-born executive has spent decades building the conglomerate’s extensive insurance businesses, which include Geico, Berkshire Hathaway Primary Group, and Berkshire Hathaway Reinsurance Group, and gained Buffett respect over the years.

In his 2017 shareholder letter, Buffett said that Jain has created “tens of billions of value for Berkshire shareholders” over his career, calling him a “proven performer.”

“If there were ever to be another Ajit and you could swap me for him, don’t hesitate,” he added.

At Berkshire’s annual shareholder meeting in 2023, Buffett again emphasized that Jain has been a critical feature of the conglomerate’s success. “We won’t have the same business if Ajit isn’t running it,” he told investors.

To his point, Berkshire’s insurance operations accounted for $83.4 billion, or around 23%, of its $364.4 billion in revenue in 2023—and more like a third of its earnings. Analysts at Morningstar noted earlier this year that half of Berkshire’s valuation comes from its insurance businesses as well.