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The reality star opened up about the ordeal via Twitter on Thursday.
"Called airline mult x to say I have fish allergy. Got on & they're serving bass," the Bravolebrity recalled.
According to Frankel, the airplane's staff claimed "they couldn't not serve it." Then the plane started "turning around." Frankel claimed she "protested" because rerouting the plane "would delay people."
"Cabin asked to not serve it & pilot made announcement to plane," Frankel continued. "That was fun. #epilife."
It's unclear if the plane ultimately reached its scheduled destination.
After getting questioned by her followers, Frankel went on to explain her allergy.
"To clarify: some allergens are transmitted by touch & air. Fish is one & is fatal," she tweeted at one point. "The more exposure to them, the more susceptible. It's not like an immunity thing where more exposure means less susceptible. It's opposite. I've always kept it quiet but that's over now."