Elon Musk has secured a funding commitment of $46.5 billion to buy Twitter Inc. and is planning to start a tender offer for its shares, a filing with the Securities and Exchange Commission showed on Thursday.

Last week, Musk announced an offer to buy the social media company for $54.20 per share, or about $43 billion. At the time, he did not say how he would finance the acquisition.

The Tesla CEO said Thursday in documents filed with U.S. securities regulators that he's exploring what's known as a tender offer to buy all of the social media platform's common stock for $54.20 per share in cash. Under a tender offer, Musk, who owns about 9% of Twitter shares, would take his offer directly to other shareholders, bypassing the board.

But Musk hasn't decided yet whether to do that.

The documents filed with the Securities and Exchange Commission say San Francisco-based Twitter Inc. has not responded to Musk's proposal.

Twitter said in a statement Thursday that it has received Musk’s updated proposal and its “new information on potential financing.”

The company said its board is “committed to conducting a careful, comprehensive and deliberate review to determine the course of action that it believes is in the best interest of the company and all Twitter stockholders.”

Last week Twitter's board adopted a “poison pill” defense that could make a takeover attempt prohibitively expensive.

Morgan Stanley the Primary Financer

The filing states that “entities related to [Musk] have received commitment letters committing to provide an aggregate of approximately $46.5 billion.”

The financing would come from Morgan Stanley and other financial institutions. Other banks involved include Barclays, Bank of America, Societie Generale, Mizuho Bank, BNP Paribas and MUFG. Morgan Stanley is one of Twitter’s biggest shareholders, behind Vanguard Group and Musk.

Musk said that $13 billion in financing came from Morgan Stanley and the other banks, as much as $12.5 billion would be loans secured by his Tesla stock, and committed $21 billion in equity, “directly or indirectly” from him, although he didn’t say what the source of those funds would be. The filing says that the equity commitment could be reduced by contributions from others or additional debt taken on.

Musk is the world’s wealthiest man, according to Forbes, with a nearly $279 billion fortune. But much of his money is tied up in Tesla stock — he owns about 17% of the company, according to FactSet, which is valued at more than $1 trillion — and SpaceX, his privately held space company. It’s unclear how much cash Musk has.

Electric car and solar panel maker Tesla allows executive officers to use shares as collateral for loans, but limits the borrowing to 25% of the value of the pledged shares. Musk owns 172.6 million shares worth $176.47 billion. Just over 51% of his stake already is pledged as collateral, according to a Tesla proxy statement. That means Musk could use the remaining stake to borrow about $21.5 billion.

Investment Banking Credibility

Getting financing from big banks brings a lot of credibility to Musk’s bid, said Wedbush Securities analyst Daniel Ives.

“This isn’t just Musk antics,” Ives said. “Banks were going to line up for this deal from the richest person in the world. The fact they they pulled it together this quick shows that Musk isn’t joking around. This is a real bid.”

Ives said the tender offer puts more pressure on Twitter’s board to find a second bidder or go to the negotiating table with Musk. “It’s a way to get around the poison pill and let shareholders speak,” he said.

A Delaware corporation named X Holdings 1 was formed at the direction of Musk and some affiliates who intend to “acquire, directly or indirectly, all of the outstanding equity interests of, or directly or indirectly merge with Twitter Inc.,” according to a financing commitment letter the company submitted.

Shares of Twitter rose slightly to $46.86 in Thursday midday trading after the financing became public. The share price is $7.34 below Musk's offer.

Musk “is seeking to negotiate a definitive agreement for the acquisition of Twitter ... and is prepared to begin such negotiations immediately,” the documents say.

'Tender' Tweets

With a tender offer, Musk would try to get other shareholders to pledge their stock to him at a certain price on a certain date. If enough shareholders agree, Musk could use that as leverage to get the board to drop the poison pill defense.

Musk signaled the possibility of a tender offer several times this week in tweets using the word “tender.”