WATCH: Biographer reveals there’s zero evidence that Trump is a billionaire – he ‘just makes it up’
Donald Trump speaking at the Iowa Republican Party's 2015 Lincoln Dinner at the Iowa Events Center in Des Moines, Iowa. (Gage Skidmore/Flickr)

Pulitzer Prize-winning journalist and The Making of Donald Trump author David Cay Johnston said in a new video that there is no evidence whatsoever that Donald Trump is actually the billionaire he claims to be.

Business Insider published the video clip, in which Johnston compared Trump's claims of extravagant wealth with actual court records and bank filings.

In 2015, Johnston said, Trump variously claimed his net worth to be $8.7 billion, $10 billion, $11 billion and higher, "even though there was nothing going on in the economy that would suggest that kind of gyrations of net worth."

"The fact of the matter is that Donald Trump just makes it up," he explained, pointing to court testimony in which Trump said he bases estimates of his net worth on his gut "feelings" and "emotional state."

Johnston said that if Trump wasn't a presidential candidate, but just someone sitting next to you on a bar stool, "you'd quickly conclude 'That's nuts.'"

In 1990, Johnston said Trump's claim of being a billionaire was fraudulent. A net worth statement drawn up by Trump's bankers declared that at that time, Trump's net worth was negative $295 million.

Today, Johnston said, it's clear that Trump is wealthy, but there is "no evidence that he is a billionaire."

"By the way, I'm having a great day today," the author quipped at the end of the video. "I think my net worth must be at least a billion dollars."

Watch the video, embedded below: