Barbara Corcoran, New York real-estate entrepreneur turned Shark Tank star, says that years ago Donald Trump lied in advertisements about the price of his company's apartments.

"He was cheating on the numbers," Corcoran told an audience at the Inc. Women's Summit in New York City on Thursday. "He made up that shit."

When Corcoran pointed out the issue to Trump, she said, he hit the ceiling.

Corcoran said Trump's ads claimed that he was building the most expensive--and by extension, most luxurious--apartments in New York City. Crunching the numbers herself revealed the apartments actually ranked closer to 10th on price, she said.

Corcoran, who at the time had begun to set herself up as an expert in the real estate space by publishing Manhattan sales rankings in The Corcoran Report, said she gave Trump a chance to see her findings before she released them to the press. Soon she was summoned to his office, she said.

Corcoran said she couldn't sleep the night before. Taking the elevator up to his office in Trump Tower, she came up with a plan. When Trump finished yelling at her, she said, she suggested that he change his ads to say the apartments were the most expensive when measured by the price per room. She said she had more expensive listings than his apartments, but they were larger.

So, she said, Trump took out a full-page ad in The New York Times with the new claim--citing Barbara Corcoran of The Corcoran Report.

"It was a publicity stunt that put me on the map," Corcoran said.