Tesla and Larry Ellison have confirmed via a new SEC filing that Ellison owns 3 million shares, which are worth about $1 billion.

The filing was necessary because Ellison agreed last week to join Tesla's board.

Tesla did not say when Ellison bought the shares, except that it was earlier this year.

However Ellison disclosed he had made a sizable investment back in October, the month when Tesla dropped near 52-week lows.

On Monday, Tesla and Larry Ellison officially reported and confirmed Ellison's precise stake in the company via an SEC filing: 3 million shares.

When Tesla announced last week that it had landed Larry Ellison as one of two new board members, the company said that he had been a believer in the company who had purchased the 3 million shares sometime earlier this year.

The filing didn't say when Ellison had bought in but at Tesla's current share price, of about $334, that stake is worth about $1 billion. And back in October, months before the board position was announced, Ellison revealed his stake. At that time, he said Tesla was his second-largest investment.

Read: Leaked Uber employee survey shows what it's really like to work at the company ahead of its massive IPO: Read the full survey results here

October was when Tesla was trading near its 52-week low, at around $250 share. That was shortly after CEO Elon Musk was slapped by the SEC over his infamous "funding secured" tweet and when investors were biting their nails over Tesla's looming need for $1 billion in cash to make a debt payment.

An outpouring of good news from the company since late October, including a profitable quarter, has since eased investors concerns and sent the stock soaring.

We don't know how much Ellison paid for his stake, but if he bought in at that low point at about $250 a share, he would have already made around $250 million. While that's pocket change for Ellison, the seventh richest man in the world worth an estimated $51 billion, it probably didn't hurt when convincing Ellison to join Tesla's board.

It will be interesting to watch how the relationship between the two men develop. Both of them are strong willed and used to being the boss. Most of Ellison's other board positions have been on companies where he was a founding investor. Some of them didn't go well. For instance, Ellison's protege, Salesforce CEO Marc Benioff, famously kicked Ellison off Salesforce's board after Ellison's company, Oracle, began to compete with Salesforce. On the other hand, Ellison was also close friends with the famously strong-willed Steve Jobs and served on Apple's board. The two never competed in business and their friendship stayed intact.

Ellison is known to respect and befriend other tough and like-minded entrepreneurs. He revealed his stake in October while he was publicly defending Musk after Musk came under fire for some controversial tweets.

And Ellison has a personal interest in sustainable energy and sustainable business, which coincides with Tesla's mission. When Ellison bought the Hawaiian island of Lanai in 2012, he said his goal was to turn the island into a "model for sustainable enterprise," using all the latest,eco-friendly technology for power and organic farming. Lanai has a large solar farm and last year, Ellison opened a high-tech indoor hydroponic organic farm.