Jeff Bezos moved quickly to capitalize on the early surge in Amazon.com Inc this year.

Bezos sold 24 million shares of the firm he founded for over $4 billion, less than two weeks after he revealed his intention to sell up to 50 million shares. The sales occurred over just four trading days, according to disclosures in regulatory filings. Prior to 2021, the second-richest person in the world had not sold any stock.

Bezos hasn’t given a reason for the sale, but the timing when he implemented the trade strategy may have revealed why. On November 2, he declared that he was relocating from the Seattle area to Miami. On November 8, he approved an alleged 10(b)5-1 plan.

Since Florida does not have a capital gains tax, Washington State implemented one in 2022, therefore Bezos’s move is probably saving him $288 million thus far in taxes. It’s reasonable to conclude that Bezos has owned Amazon stock from the company’s founding because he has only ever purchased one share. As a result, nearly all of the stock’s worth would be regarded as capital gains.

As of Monday’s close—the last day which Bezos sold shares—Amazon shares had risen 13% year to date, per a filing. On Tuesday, they dropped 2.2% to $168.64.

Representatives for Bezos and Amazon declined to comment.

A $288 million tax bill would be a huge windfall for Washington, which according to state officials made $855 million in capital gains tax revenue last year, more than 50% of which came from only ten individuals.

There has been opposition to the tax in the state. Billionaire Ken Fisher, who has criticized the tax and the court ruling that upheld it, said in March that he was moving his company from Washington to Texas.

Voters may encounter a ballot measure in November that would allow them to vote to remove the tax.