Billionaire Elon Musk has offered to buy Twitter for about $41 billion, just days after rejecting a seat on the social media company’s board.

Musk’s offer price of $54.20 per share, which was disclosed in a regulatory filing on Thursday, represents a 38% premium to Twitter’s April 1 close, the last trading day before the Tesla CEO’s more than 9% stake in the company was made public.

Twitter’s shares jumped 12% in premarketing trading, Reuters reported.

“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.

“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 added.

Earlier this week, Musk said he had abandoned a plan to join Twitter’s board, just as his tenure was about to start. Taking his board seat would have prevented him from a possible takeover of the company.