Elon Musk, billionaire CEO of Tesla and SpaceX, has offered to buy the social media company Twitter.

The filing showed Musk was offering to pay a total of $41.39 billion (€37.92 billion) to buy the platform. That amounts to $54.20 per share, up 38% on the price per share before Musk bought over 9% of shares on April 1. Twitter’s share price jumped markedly in pre-market trading, already approaching the value Musk had offered.

“Since making my investment I now realize the company will neither thrive nor serve this societal imperative in its current form. Twitter needs to be transformed as a private company,” Musk said in a letter to Twitter Chairman Bret Taylor, seen by Reuters.

“My offer is my best and final offer and if it is not accepted, I would need to reconsider my position as a shareholder,” Musk said.

He also said that he would not be joining Twitter’s board of directors as announced by the company’s CEO Parag Agrawal. Musk became the social media platform’s biggest shareholder — owning 9.5% of shares — after spending $2.9 billion. The position on Twitter’s board would have limited him to owning no more than 14.9% of the company and would have obliged him to act only in the company’s best interests. The billionaire had tweeted several suggestions for the platform after buying the shares, including making Twitter free of advertising, despite ads bringing in almost 90% of the company’s revenue.