(Bloomberg) — After an astronomical rally on its first trading day, VinFast Auto Ltd. Now to the ground – erasing a large chunk of its billionaire founder’s fortune.

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The Vietnamese electric car maker has fallen sharply over the past three trading days in New York, chipping away at more than half of the 255% gain it made on Tuesday when it listed on Nasdaq Global Select Market.

Chairman and founder Pham Nhat Vuong, who controls all but a handful of the company’s shares, has seen his net worth drop nearly 53% to $21 billion, according to the Bloomberg Billionaires Index.

VinFast’s market capitalization also slumped, dropping to $37.4 billion from its peak of $85 billion, when it was briefly ahead of General Motors despite being on track to generate fewer sales this year than GM does in a week.

Large fluctuations in stock prices were expected. Vuong controls 99% of VinFast shares, mostly through his business conglomerate, Vingroup JSC. This leaves a small portion of other investors to trade, which means that even relatively small transactions can have a significant impact on the price.

However, Vuong doesn’t hurt. Since Bloomberg Index didn’t account for his stake in VinFast until the company completed its merger with the blank-check company this week, he’s still richer than he was before the listing.

On paper, he earned close to $40 billion on his first trading day – one of the biggest leaps in wealth the index has ever recorded.

— with assistance from Tom Maloney.

(Updates to reflect Friday trading)

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