Donald Trump’s business empire was supposed to be in peril as never before on Monday (US time). Instead, it turned into the single-greatest day on record for the former president’s wealth.

As he faced a deadline to post a bond of more than $US500 million ($764 million) in a New York fraud lawsuit, a state appeals court tossed him a lifeline, slashing the amount he’d have to post to $US175 million — an amount he says he’ll cover. Around the same time, his social media company Trump Media & Technology Group wrapped up a 29-month merger process, meaning shares worth billions of dollars on paper are now officially Trump’s.

All told, his net worth will increase by more than $US4 billion. That means for the first time ever, Trump is set to join the ranks of the world’s wealthiest 500 people on the Bloomberg Billionaires Index, with a fortune of $US6.5 billion ($10 billion).

“We have a great company and are incredibly honoured,” Eric Trump, executive vice president of the Trump Organisation, said in a statement.

A representative for Donald Trump did not respond to a request for comment.

Trump, 77, has been rich all his life. But his fortune, which previously peaked at $US3.1 billion, has largely consisted of real estate, creating a potential financial crisis ahead of Monday’s deadline to either pay his $US454 million verdict or post a bond for 120 per cent of the judgment. New York Attorney-General Letitia James signalled she was ready to seize assets if Trump did not comply.

Trump vowed to quickly post cash or a bond to cover the lowered amount. As it stands now, he can’t cash in on his windfall from Trump Media’s merger with Digital World Acquisition Corp because his shares are locked up for roughly six months.

The latter’s shares closed at $US49.95 on Monday and are up about 190 per cent since the start of the year. That values Trump’s 58 per cent stake in the company at about $US3.9 billion. (It’s expected to start trading under the ticker DJT on Tuesday in New York.)