Sky Xu, the reclusive billionaire behind Shein Global Holdings Ltd., once commanded a net worth of more than $23 billion as the fast-fashion titan soared past the parent companies of H&M and Zara. But in just four years, Xu’s fortunes have taken a sharp turn. As Shein gears up for its Hong Kong listing on Tuesday, the company’s valuation has shrunk to roughly a quarter of its 2022 peak of $100 billion. Xu’s 30% stake now clocks in at about $8 billion, according to the Bloomberg Billionaires Index—a decline of over $15 billion.

Part of the downfall stems from poor timing. Over the past year, a wave of Chinese consumer brands debuted to strong investor interest, only to be overshadowed by a slew of artificial-intelligence companies that captured the market’s imagination and minted new billionaires. “They definitely missed the window,” said Sam Wyatt, an international-equities portfolio manager at U Ethical Investors in Melbourne. E-commerce has lost its allure compared to the AI narrative, he noted.

The performance of Hong Kong IPOs has been mixed. Drinks maker Eastroc Beverage Group Co. and pig breeder Muyuan Foods Co. both trade below their listing prices despite billion-dollar debuts. The brothers behind Mixue Group, a bubble-tea chain, have seen their wealth shrink by more than a fifth since going public last year. A Shein spokesperson declined to comment.

Xu, 43, launched Shein in 2012 with three partners, all former colleagues at a search-engine marketing firm. They leveraged their digital expertise to build a retailer known for cheap, trendy clothes. The business boomed during the Covid-19 pandemic, fueled by young shoppers. But revenue growth has since slowed, as disclosed in July ahead of the IPO.

A key strategy—avoiding US and European import taxes through small parcel shipments—was upended last year when the Trump administration ended a crucial tariff exemption and the European Union imposed a fixed customs duty on small packages. “The direction of the market is changing, not in Shein’s favor, especially in the recent years,” said Sheng Lu, a professor of fashion and apparel studies at the University of Delaware. AI is also leveling the playing field, enabling competitors to respond more quickly to shifting consumer tastes.

Shein attempted to go public at its peak but faced hurdles in New York and London amid scrutiny over labor practices. Its supply chain is rooted in China, yet the US and Europe are its key markets. Executives distanced the brand from its Chinese origins and moved the global headquarters to Singapore, but they still needed Chinese regulators’ approval for an IPO. “Shein was the hottest topic two to three years ago—a Chinese firm that could have IPO’ed in the US because it already had a strong fast-fashion brand and consumer recognition,” said Jason Hsu, chief investment officer at Rayliant Global Advisors. “But the hot topic now is AI.”