Today, global fast-food chain Burger King debuted a vegan-friendly version of its iconic Whopper to 59 locations in and around St. Louis, MO. The chain partnered with plant-based startup Impossible Foods to create the new meatless option using the Impossible Burger 2.0, a new and improved version of Impossible Foods’ popular plant-based patty. The Impossible Whopper features the flame-grilled vegan patty topped with sliced tomatoes, lettuce, mayonnaise, ketchup, pickles, and sliced onions on a toasted sesame-seed bun—which can be made vegan if ordered without the mayonnaise. Though the announcement comes on April Fools Day, Impossible Foods founder Patrick Brown confirmed the launch is real: “You can think of it as a meta April Fool’s joke in the sense that people will get a burger that they will actually believe is made from animals and be told it’s made from plants,” Brown said. “They’ll think it’s an April Fool’s joke, and it’s not.” If the new menu item is successful, Burger King plans to expand the offering to its more than 7,000 locations across the United States later this year, creating what will become the biggest restaurant expansion for Impossible Foods. Currently, Impossible Foods’ restaurant partners collectively serve the burger at more than 5,000 locations nationwide, including fast-food chain White Castle, which started selling the patty last year as a vegan-friendly Impossible Slider at its 377 locations nationwide. “It’s something that can be a real milestone for us as a brand,” Burger King Global Chief Marketing Officer Fernando Machado told media outlet Forbes. “It’s definitely a milestone for Impossible Foods.” Earlier this year, competing chain Carl’s Jr. added the Beyond Famous Star—a vegan-friendly version of its iconic burger made with vegan patty Beyond Burger—to more than 1,000 locations nationwide.