Elon Musk approached SpaceX, the rocket company he runs as CEO, for a $1 billion loan around the time he bought Twitter. 

The unusual loan is the most recent illustration of how the world's richest man has raised money from his empire of businesses without having to permanently give up shares, allowing him to fund his diverse range of endeavors.

According to documents analyzed by reporters, Musk drew the entire loan down in October after SpaceX approved it and backed it with some of his SpaceX stock.

The reason he took up the loan is unknown. Shortly after taking out the financing, he paid it back, giving SpaceX $1 billion plus interest in November. Requests for comments from Musk and SpaceX were not answered.

For years, Musk has had agreements with financial institutions to borrow money against the shares of his businesses, including Tesla, of which he is the CEO. His lender at privately held SpaceX has been the corporation itself.

According to a SpaceX filing with the Federal Communications Commission, Musk is by far SpaceX's largest stakeholder, holding a 42% stake and about 79% of the company's voting power as of March. He almost definitely has the option to borrow money from SpaceX if he so chooses.

In the previous year, borrowing took place as SpaceX made significant investments in both its Starship rocket program and Starlink, a satellite internet company. To help pay for both, the business has raised significant sums from investors, and Musk has urged staff to be frugal with their expenditures.