Elon Musk’s wealth took a major hit on Thursday, as the share price of Tesla, his electric car company, fell sharply. Musk’s net worth fell by $20.3 billion, according to the Bloomberg Billionaires Index, the seventh-largest single-day decline on record.

The sell-off in Tesla shares was triggered by a warning from the company that it may have to keep cutting the prices of its electric vehicles. Tesla said that it is facing increasing competition from rivals, and that it needs to lower prices in order to maintain its market share.

The decline in Tesla’s share price also had a knock-on effect on Musk’s personal wealth. Musk owns about 17% of Tesla, so the drop in the company’s stock price caused his net worth to decline by a corresponding amount.

As a result of the sell-off, Musk is no longer the world’s richest person. He is now ranked second, behind Bernard Arnault, the chairman of luxury goods maker LVMH.

The decline in Musk’s wealth is a reminder that the fortunes of the world’s richest people are closely tied to the stock market. When the stock market goes down, so does the wealth of the billionaires.

It remains to be seen whether Musk’s wealth will recover in the coming months. However, the sell-off in Tesla shares suggests that the company is facing some challenges. If Tesla is unable to maintain its market share, Musk’s wealth could continue to decline.