The founder of the celebrated restaurant on the ninth floor of Barneys was escorted out of the building Monday after lambasting the luxury retailer’s management to The Post.

Before being shown the door, Mark Strausman, who launched Freds in 1996 at the behest of the grandson of Barneys’ founder, said goodbye to his staff and loyal customers. He received a standing ovation, sources said.

Strausman called his canning from Freds “emotional” but not surprising, and then lit into the troubled retailer’s management yet again.

“Honestly, I’m not shocked because it’s pretty true to form,” he said. “This is how organized they are. They turn off your email but my electronic pass still let me into the building. This is par for the course. They can’t even fire people correctly. I’m shocked, but not.”

“Mr. Strausman was working for Barneys as a consultant at Freds Madison Avenue. His contract was terminated after he made disparaging and unprofessional comments about Barneys,” a company spokesperson said.

The firing comes one day after The Post reported the 62-year-old chef’s sore feelings about the management that placed the company in federal bankruptcy protection in August. In the story, Strausman pointed a finger at hedge fund manager Richard Perry, whose Perry Capital took over the department store chain in 2012. He said Perry’s managers unnecessarily meddled with Freds, including changing the brand of coffee it used and removing the chicken livers from the menu.

Neither Perry nor the fund, which shuttered in 2016 but retained its stake in Barneys, returned comment.

Barneys regulars jumped to defend Strausman, whose recipes have attracted celebrities like Larry David, Bruce Springsteen and David and Victoria Beckham.

“Mark made that place. They should have more loyalty,” one regular griped.

He’s “the toast of the town,” said another.

Starting in March, his followers will find him at a new eatery, Mark’s Off Madison at 41 Madison Ave. “I’m a chef, and in a couple of months I’ll be cooking again. That’s what counts.”