Tesla CEO Elon Musk has purchased 9.2 percent of Twitter, a Monday SEC filing said.

Musk, with 73.5 million Twitter shares, is now the social media company's largest shareholder.

Reacting to the news of Musk’s nearly 10 percent stake in Twitter, the site's shares increased over 25 percent on Monday, Fox News reported.

By Monday morning, shares had jumped to $49.81.

Musk bought the shares days after criticizing Twitter for failing to protect free speech.

“Free speech is essential to a functioning democracy,” Musk tweeted. “Do you believe Twitter rigorously adheres to this principle?”

“Is a new platform needed?” he asked.

“Given that Twitter serves as the de facto public town square, failing to adhere to free speech principles fundamentally undermines democracy,” Musk tweeted. “What should be done?”

Musk has around 80 million followers on Twitter, some of whom urged him to buy Twitter or create his own alternative.

In late March, Musk tweeted that he was “giving serious thought” to creating his own social media platform to compete with Twitter.