Steve Ballmer, who dropped out of Stanford business school to become the 30^th employee at Microsoft, is on the verge of eclipsing his mentor Bill Gates in wealth—thanks to his successor.

A prescient bet on ChatGPT creator OpenAI made by current CEO Satya Nadella has helped to catapult the value of Ballmer’s estimated 4.5% stake in the company. The largest single individual shareholder is now within reaching distance of his mentor as Gates sold the bulk of his Microsoft stock as he shifted his focus to philanthropy.

According to Bloomberg, Ballmer is now worth $117 billion, just six billion short of Gates, whose money is managed by Cascade Investments (Forbes currently judges the gap between them to be slightly higher). This earns Ballmer the distinction of being the only centibillionaire to have made his fortune as an employee rather than entrepreneur.

Ballmer, who met Gates at Harvard undergrad and went on to become his assistant tasked with professionalizing the then-startup, ran the company from 2000 after the co-founder took on a titularly junior role in charge of software development. Ballmer has gone on the record to say he still struggled to steer the company under the shadow of Gates until the latter departed eight years later.

Ballmer himself stepped down in 2014 following a strategic difference with the board. At the time, the company’s stock price doldrums reflected its clashes with antitrust authorities as well as its failure to compete with Apple in the consumer electronics hardware space.

“I blew that,” Ballmer admitted five years ago, as he acknowledged never anticipating the revolutionary success of the iPhone due to its premium price.

Ballmer less known for his charitable work

While some developments initiated during Ballmer’s tenure continue to be a staple feature of the company’s hardware business—most notably the Xbox gaming console and the Surface tablet—the iPod competitor Zune flopped hard and was eventually pulled from the market.

Thankfully for Ballmer, successor Satya Nadella has reinvigorated Microsoft’s stock price and grew it into a company worth well over a trillion dollar with the help of its booming cloud computing operations and, most recently, its investment in OpenAI.

But Ballmer will never be able to eclipse his mentor when it comes to giving his fortune away to charity.

Since stepping back in 2008, Gates has gone on to be a major philanthropist, donating billions in particular through his foundation that has sought to eradicate infectious diseases in developing nations.

Ballmer, who “drifted apart” from Gates in the years that followed, has a charitable group of his own focused on improving social mobility for economically disadvantaged children. Yet his post-Microsoft endeavors have been best known through his acquisition and ownership of the L.A. Clippers basketball team, which he purchased for $2 billion in 2014.

This story was originally featured on Fortune.com