Tesla CEO Elon Musk, the world’s richest person, sold a massive chunk of stock on Monday to help pay taxes on options he received nearly a decade ago, new regulatory filings showed Wednesday—just days after the eccentric billionaire suggested he’d make the rare sale in response to a billionaire tax proposal discussed last month in Washington, D.C.

In two filings released Wednesday by the Securities and Exchange Commission, Musk disclosed he exercised nearly 2.2 million stock options worth about $2.2 billion for roughly $13.4 million on Monday and then went on to sell about 934,000 shares for just over $1.1 billion.

Musk sold the shares at an average price of about $1,170—securing a nearly 180% runup in prices over the past year but still about 6% shy from an all-time high on Thursday.

The move comes after Musk on Saturday called on Twitter users to help decide whether he should sell 10% of his roughly 23% stake in Tesla in response to a short-lived proposal in Congress that would have taxed billionaires’ unrealized stock gains to help curb tax avoidance among the ultrawealthy.

Though users overwhelmingly voted for Musk to make the sale, footnotes in the Wednesday regulatory filings reveal the 50-year-old previously planned to sell the shares on September 14 to help foot the bill for options scheduled to expire next year.

Musk did not immediately respond to Forbes’ request for comment.

This is only the third time Musk has sold Tesla stock since the company went public on the Nasdaq exchange in 2010—and it’s easily his biggest transaction. In July 2010, Musk sold slightly more than 1.4 million shares for $24 million, and in 2016, he sold another 2.7 million shares for about $593 million.