In this photo illustration, the new Impossible Whopper sits on a table at a Burger King restaurant on August 8, 2019 in Brooklyn, New York.

Burger King is doubling down on meatless burgers.

The Restaurant Brands International chain announced on Monday plans to launch a vegetarian burger in more than 20 markets across Europe. The Rebel Whopper, made with patties from Unilever-owned The Vegetarian Butcher, will be available in more than 2,400 European locations Tuesday.

Burger King first launched the Rebel Whopper and another meatless sandwich, the Rebel Chicken King, in Sweden earlier this year.

In the United States, the burger chain will test substituting beef patties with Impossible patties in its Whopper Jr. burgers and signature hamburgers. The company said 180 restaurants in Milwaukee, Cedar Rapids, Augusta, Cincinnati and Buffalo will test the extended Impossible burger line.

Thanks in part to the success of the Impossible Whopper, Burger King's U.S. same-store sales grew by 5% during its third quarter, its largest jump since 2015.

"The Impossible Whopper is a huge hit with our guests and has quickly become one of the most successful product launches in Burger King's history," Restaurant Brands CEO Jose Cil told analysts on the company's conference call in October.

Cil also said on the call that the company is working on meatless products for Latin America and Asia as well.

Burger King's announcement comes as some of its biggest competitors have been slower to jump on the meat alternative trend. McDonald's is testing a burger made with Beyond Meat patties at select locations in Ontario, Canada, while Wendy's is testing black-bean burgers.

Restaurant Brands' stock, which has a market value of $31 billion, is up 28% so far this year. Shares of McDonald's, valued at $148 billion, have risen 8% in the same period, while Wendy's stock, which has a market value of $5 billion, has jumped 33% year to date.