Shares of Twitter Inc. soared 12.2% in premarket trading Thursday, after Tesla Inc. “Technoking” Elon Musk disclosed a proposal to buy all of the outstanding shares of the social media company he doesn’t already own for $54.20 each. That represents an 18.2% premium to Wednesday’s closing price of $45.85. With 800.64 million shares outstanding as of Feb. 10, Musk’s bid would value Twitter at $43.39 billion. The disclosure comes in a 13D/A filing with the Securities and Exchange Commission early Thursday, in which Musk confirmed his previous disclosure of owning 73.12 million Twitter shares, or 9.1% of the shares outstanding. The filing said Musk had delivered a letter containing the “non-binding proposal” to Twitter, but says there can be no assurance that a definitive agreement will be executed. Twitter’s stock has gained 6.1% year to date through Wednesday, while the S&P 500 has lost 6.7%.

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