Billionaire Elon Musk has offered to buy social media company Twitter, according to a regulatory filing.

The Tesla owner’s offer of $54.20 per share represents a 38% premium to the closing price of Twitter’s stock on 1 April 1, the last trading day before his 9.2% stake in the company was made public.

His approach to the Twitter board, valuing the company at $43 billion, follows reports yesterday that he was being sued because he failed to announce that he had bought a major stake in company under market rules.

Mr Musk, who has a personal fortune in excess of $250 billion, bought the shares on 14 March, according to the latest reports, but did not notify the Securities and Exchange Commission until 4 April.

The Tesla and SpaceX billionaire, who is now the largest shareholder in Twitter, faces legal action from investors in a New York federal court.

Musk has informed the board of Twitter: “I invested in Twitter as I believe in its potential to be the platform for free speech around the globe, and I believe free speech is a societal imperative for a functioning democracy.”