Shares of the biggest online retailer dropped 8.1% to US$1,637 in extended trading at 4.24pm in New York. At that price, Bezos would have a net worth of US$102.8 billion, ranking him second, and almost US$5 billion behind Gates, according to the Bloomberg Billionaires Index.

Bezos took the top spot from the Microsoft Corp co-founder in October 2017. The ranking officially updates after the close of each trading day in the US, so the change won’t be official until today’s market close.

Microsoft, the world’s most valuable company, has surged 38% this year, boosting the value of Gates’ 1% stake and bringing his fortune to US$107.5 billion. The rest of his wealth is derived from share sales and investments made over the years by his family office, Cascade.

Gates, 63, remains an aggressive stock investor, with more than 60% of his portfolio in equities, he said last month in a Bloomberg Television interview.

Bezos, 55, would still be ranked No 1 if he and MacKenzie Bezos hadn’t divorced. The pair announced their split in January, with MacKenzie, 49, receiving a quarter of their Amazon holdings in July.

Her net worth would drop to US$32.9 billion with Amazon shares priced at US$1,637, and she’d remain the world’s fourth-richest woman.

Gates, on the other hand, may have never relinquished the top spot were it not for his philanthropy. He has donated more than US$35 billion to the Bill & Melinda Gates Foundation since 1994.