Google cofounder Sergey Brin might pocket over $100 million by selling his Tesla stock, after plowing $500,000 into Elon Musk's automaker before it went public

• Sergey Brin, an early Tesla investor, is set to sell his stake, The Wall Street Journal reported.
• He's cashing out after Elon Musk reportedly had an affair with his wife. Musk has denied the claim.

Sergey Brin, an early Tesla investor, may be poised to pocket over $100 million by cashing out his stake in Elon Musk's automaker.

The Google cofounder and former Alphabet president has instructed his financial advisers to sell his personal positions in Musk's companies, after the Tesla CEO had a brief affair with Brin's wife that spurred Brin to file for divorce earlier this year, The Wall Street Journal reported on Sunday, citing people familiar with the situation.

The Journal was unable to learn the size of Brin's investments in Musk's businesses, or whether he's disposed of them already. Tesla and Alphabet didn't immediately respond to requests for comment from Insider. Musk has dismissed claims of an affair as "total BS" on Twitter.

Brin bet an unknown amount on Tesla in 2006, helping the nascent electric-vehicle company to raise a total of $40 million. He plowed another $500,000 into the carmaker in December 2008, as part of another $40 million fundraising that was "enough to keep the lights on just a little while longer," author Hamish McKenzie wrote in "Insane Mode: How Elon Musk's Tesla Sparked an Electric Revolution."

However, Brin's name doesn't appear in any of Tesla's SEC filings, indicating he's never owned more than 5% of the company, and didn't sell any shares when it went public in June 2010. As a result, the size and value of Brin's Tesla stake, and whether he's sold it, remains unclear.

Still, if we conservatively assume that Brin owned $500,000 of Tesla stock following the company's IPO, his stake would be worth over $100 million today. Tesla shares have skyrocketed from below a split-adjusted $4 when they were first listed in 2010, to over $800 as of Friday's close - a roughly 200-fold gain.

Tesla's soaring stock price has generated huge gains for other shareholders too. Oracle cofounder Larry Ellison, who announced in June that he was stepping down from Tesla's board, owned about 15 million shares of the company as of March 31. He spent about $1 billion on this position, which is now valued at north of $12 billion.

Moreover, Musk owned 265 million Tesla shares at the last count — a stake worth $217 billion as of Friday's close.

Read more: Tesla earnings: Time to top-up on shares in Elon Musk's car maker or bail out? 3 experts weigh in on its prospects and reveal an updated price target.