The Real Housewives of Atlanta star Porsha Stewart had an embarrassing moment on Sunday night's episode when she got a historical fact completely wrong.

When the ladies of the Bravo show went on a Freedom Trail tour in Savannah, the reality star revealed that she thought the Underground Railroad was an actual train.

As the tour guide showed the women ventilation holes on the floor, he said, "So this is where they used to catch air as they were moving below us... To this day we don't know how they got in or out from the inside of the church."

Stewart then responded, "Well there has to be an opening for the railroad at some point because somebody is driving the train."

Some of the fellow housewives were flabbergasted by Stewart's confusion over the term used to describe the network of people who helped the fugitive slaves escape to the North and to Canada in the 19th century.

"It wasn't a train, baby," Phaedra Parks told Porsha. "It wasn't a train at all. That is just a euphemism."

Kenya Moore, who was clearly appalled by the remark, told the cameras: "It's almost hurtful to me, to watch her be so dumb."

She then took to her blog to speak on the matter in more depth and also pointed out that Stewart's deceased grandfather was Hosea Williams, a well-known civil rights activist in Atlanta.

"Porsha is an embarrassment to her grandfather, his legacy, her family, and most importantly, herself," she wrote. "Our educational system has failed her, anyone who coddled her or encouraged her to focus on her makeup, weave, and shoes to find a man to take care of her rather than her education has failed her."