Elon Musk's net worth dropped by a staggering $16.3 billion (£12.6bn) on Tuesday - the largest single-day loss in the history of the Bloomberg Billionaires Index.
He's still worth $82.2bn (£63.5bn), so he's probably not going to worry too much, but the Tesla boss saw his electric car company's value fall by 21 percent in New York trading, after news broke of a partnership between two of his competitors.
Nikola Corp. and General Motors Co. joined forces, creating a perceived threat to Musk's Tesla.
The massive drop just shows the volatility of the stock market during the pandemic, with nothing certain in the business world.
Just last week (1 September), Musk became the third richest person in the world after overtaking Facebook founder Mark Zuckerberg.
According to Bloomberg's Billionaire Index, Musk slid into the third spot and was worth an unfathomable $115bn (£85.6bn), while Zuckerberg dropped to fourth place with $111bn (£82.7bn).
The boost to his wealth came from a 500 percent rise in Tesla stocks, which saw an extra $87.8bn (£65.4bn) added to his fortune this year.
Tesla stocks hit an all time high at the end of last month, at $2,213 (£1,650) per share.
They're now sitting around the $500 (£370) mark following a 'forward split', where a company multiplies the amount of shares each person holds.
These splits don't see the company lose any value, but they do lower the value of each individual share. It was hoped that these new lower cost shares would encourage more investors to splash their cash with the company.
At the end of August, Musk also revealed fresh details about his much-anticipated Neuralink brain chip, describing the device as 'kind of like a Fitbit in your skull'.
He then presented a pig who had been fitted with one of the devices.
Introducing Gertrude to the viewers, Musk said: "We have a healthy and happy pig, initially shy but obviously high energy and, you know, kind of loving life, and she's had the implant for two months."
He also took questions, with one person asking if the chip meant there could be a possibility to 'save' and 'replay' human memories in the future.
Musk replied: "Yes, I think in the future you'll be able to save and replay memories.
"I mean, this is obviously sounding increasingly like a Black Mirror episode. But... well, I guess they're pretty good at predicting."
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