“Twitter needs to be transformed as a private company,” said billionaire Tesla CEO Elon Musk.

Updated at 6:48 am EST

Twitter  (TWTR) – Get Twitter, Inc. Report shares surged higher Thursday after billionaire Tesla  (TSLA) – Get Tesla Inc Report CEO Elon Musk offered to buy the social media group for around $42 billion just days after declining to join the board.

Musk said his offer, which he called ‘best and final’ would value Twitter at $54.20 per share, adding that he intends to take the company private if his acquisition is successful. If it is not successful, Musk said, “I would need to reconsider my position as a shareholder.”

“I invested in Twitter as I believe in its potential to be the platform for free speech around the global, and I believe free speech is a societal imperative for a functioning democracy,” Musk wrote in his Securities and Exchange Commission filing.

“However, since making my investment I now realize the company will neither thrive nor serve this societal imperative in its current form, he added. “Twitter needs to be transformed as a private company.”

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Twitter shares were marked 12.2% higher in pre-market trading to indicate an opening bell price of $51.45 each, a move that would extend the stock’s one-month gain to around 55.6%.

Musk, who unveiled a 9.1% stake in the micro-blogging website last week, was due to assume his seat on the board Saturday and had spoken publicly of his desire to bring “significant improvements” to the company. 

That promise has lead to reports of anxious employees at the group’s San Francisco headquarters, as well as a move by CEO Parag Agrawal to arrange a so-called ‘Ask Me Anything’ session with the newest board member.

Agrawal, however, said late Sunday that Musk has “declined to join our board” following what he called “many discussions”, but declined to elaborate in terms of how the decision was taken.

Musk’s relationship with Twitter — which he called a “war zone” during his 60 Minutes interview in 2018 — remains complicated, in that he is both a prolific user of the site — with more than 80 million followers — as well as one of its more vocal critics.

Late last month, Musk said he was giving ‘serious thought” to starting his own social media company, and accused Twitter of “failing to adhere to free speech principles fundamentally undermines democracy” given that the site “serves as the de facto public town square.”