MIAMI — What started as the “McWhopper proposal,” a peace offering from Burger King to McDonald’s to raise awareness for Peace Day, has developed into a much larger partnership. After several restaurants approached Burger King to unite in honor of Peace Day on Sept. 21, a momentous decision was made and the Peace Day Burger was born.

This culinary mashup of a lifetime will contain of parts of Denny’s Bacon Slamburger, Wayback’s Wayback Classic, Krystal’s Cheese Krystal, Giraffas’ Brutus and Burger King’s Whopper sandwiches.

The Peace Day Burger will be offered for one day only in Atlanta at a pop-up restaurant on 1122 Northside Dr., with the sole objective of raising awareness for Peace Day and the Peace One Day organization. The Peace Day Burger will be available from 11 a.m. to 6 p.m. free of charge (1,500 sandwiches are available, first-come, first-served). All participating burger brands will be furthering the cause with a direct monetary donation to Peace One Day.

“Since the beginning, the main objective of this initiative was to raise awareness of Peace Day. We are really proud to be part of the Peace One Day corporate coalition and to see that the awareness of Peace Day in the U.S. is almost five times higher among those who saw this campaign than those who were not aware of it,” said Fernando Machado, senior vice president for Global Brand Management at Burger King Corp., Miami. “We were overwhelmed by the goodwill of our fellow restaurateurs and believe that working with them to create this once-in-a-lifetime burger is a beautiful twist of fate.”

After Burger King initially expressed interest in working with McDonald’s to create the “McWhopper,” McDonald’s CEO Steve Easterbrook took to Facebook to say, “We love the intention but think our two brands could do something bigger to make a difference.”

“As far as McDonald’s goes, any activity they undertake, whether in partnership with Burger King or on their own, would be incredible, as it will raise further awareness for Peace Day,” Machado said. “And inadvertently, the McWhopper has 100% become a reality for some. The public wholeheartedly embraced the campaign and thousands of DIY McWhoppers have been created, reviewed and shared on social media.”

Since launching the McWhopper campaign, Peace One Day has seen an unprecedented upswing in people talking about Peace Day, in traditional and social media. Burger King and its new allies are confident they will increase this exposure even further with the Peace Day Burger.

Peace Day is a day of ceasefire and nonviolence unanimously adopted by all UN member states, following a successful campaign by the nonprofit organization Peace One Day. “Our short-term goal is to expose 3 billion people to Peace Day by 2016. It’s a big target but it’s very possible, particularly with the support of the corporate sector. They have the resources and ability to raise awareness on a massive scale. That awareness creates action, and that action saves lives,” said Jeremy Gilley, founder of Peace One Day.

Burger King is now part of Oakville, Ontario-based Restaurant Brands International, created by the private-equity group 3G Capital when it merged the burger chain with Tim Hortons, a Canadian doughnut and coffee chain.