Wang is the 15th billionaire shareholder of Ant Financial. Twelve others emerged on Jan 30 after the company's valuation doubled to about $50 billion amid plans for a private placement ahead of an initial public offering, people familiar with the matter said.

The billionaire may be holding the shares for her son, according to James Hu, a Shanghai-based analyst at Capital Securities Corp.

"It's common for family members to hold shares for each other," Hu said. "It could be for various reasons such as a single shareholder's stake-size limit."

Wang is the mother of David Yu, who co-founded Yunfeng Capital with Ma, according to earlier filings by Huayi Brothers Media Corp. Yu and Ma are on the board of the Beijing-based film distributor. Yu also holds shares of Ant Financial, the filings showed.

Jenny Kong, a spokeswoman for Yunfeng Capital in Shanghai, did not respond to phone calls and an e-mail seeking comment from Yu and Wang. Yu also did not respond to a message sent to his microblog account.

Wang's stake in Ant Financial is held through a company established in December, according to the filings. That entity became a shareholder of Ant Financial about two weeks ago, obtaining its stake from the partnership that is owned by Ma and Xie, the filings showed.

"E-finance products are flourishing," Elinor Leung, a Hong Kong-based analyst with CLSA Ltd, said in a report last week. Products such as online payment, consumer financing and Internet banks "gained full support from the government after a cleanup last year as it provides much needed funding alternatives to fuel private sector growth".

Yunfeng Capital is a combination of co-founders Ma and Yu's first names in Chinese, Yun and Feng respectively, according to its website. Set up in 2010, the Shanghai-based company counts more than 10 Chinese entrepreneurs among its co-founders, including New Hope Group's billionaire Chairman Liu Yonghao and Giant Interactive Group Inc's Shi Yuzhu.

Alipay was spun off by Ma in 2011 because a transfer into Chinese ownership was necessary to facilitate applying for an online payment license in China, Alibaba had said. Alipay processes payments for e-commerce companies and has more than 800 million registered users. It handles 45 million transactions a day, the company said in October.

Under a revised agreement, Alibaba is entitled to a payment of at least $9.4 billion if Alipay or its parent stages a public offering. Alibaba also gets the perpetual right to 37.5 percent of the finance arm's pretax earnings and can buy a stake of about one-third if regulators approve the listing.

New billionaires from the latest valuation of Alipay's parent include Alibaba's Chief Executive Officer Jonathan Lu and Chief People Officer Lucy Peng.