Donald Trump's "genius factor" could have added billions of dollars to the actual value of his property portfolio, an expert witness told the former president's fraud trial Monday.

Frederick Chin, who was called by the defense as an expert in real estate valuation, said Trump was using the "as if" investment value to put a price on his holdings, and not the "as is" market value, ABC News reported.

Trump and his associates are on trial in New York for exaggerating the value of their real estate in an effort to secure loans and insurance. Judge Arthur Engoron has already found them liable for fraud, meaning the trial is largely to determine damages.

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Chin said the "as if" value allowed a developer to consider future plans for the property when setting its value. He gave an example of a vacant lot in New York City with a market value of $500 million, which could be seen to have a value of $2 billion to a developer who wants to build a hotel there.

ABC News reported that Engoron referred to Chin's description as a developer's "genius factor."