An English McDonald's customer said she immediately vomited after biting into her Vegetable Deluxe burger and finding it contained chicken.
Louise Davies, 50, hadn't eaten meat for 45 years before her fateful trip to a franchise in Gloucester, Gloucestershire Live reported.
She went to the restaurant's drive-thru with her 11-year-old daughter and ordered the burger, which is supposed to contain two red pepper and pesto goujons, just after 5pm.
But when she bit into it, Davies was horrified to recognise the taste of chicken.
"I immediately was sick because I haven't eaten meat in over 40 years," she told Gloucestershire Live.
"The texture and everything... That's the effect meat will have on me. Even the smell of it I don't like. I didn't think to look in it, I just thought it was a veggie burger.
"I now can't trust anything from McDonald's to be vegetarian. I feel upset and a bit betrayed."
In a statement to Newsweek, a McDonald's spokesperson apologised "for the mistakes that were made in this case".
"We have a number of procedures in place to avoid inaccurate orders, but in this case these were clearly not followed, and we are looking into why this occurred."
