Burger King is trying to bury the hatchet with its biggest competitor, international burger chain McDonald’s. After decades of rivalry, Burger King thinks it has found the solution and it’s in a burger.

On August 26, Burger King proposed an unusual collaboration to McDonald’s: create a burger together, which they would have named McWhopper.

Burger King introduced its proposal to the world with full-page ads and with a website created for the occasion, mcwhopper.com. On it, the company said the “invitation might be unexpected but is 100 percent sincere.”

The idea is to make it together and sell it for one day, Peace Day (September 21 ) in one location. The place Burger King chose was Atlanta, which is geographically midway between each company’s headquarters —McDonald’s has its headquarters in Chicago and Burger King in Miami.

The aim of the McWhopper proposal was to make noise and create awareness for Peace Day. Proceeds of the sales of the McWhopper would be donated to Peace One Day, a nonprofit international organization which collaborated with Burger King on the proposal.

McDonald’s posted its response on Facebook and on Twitter, though its CEO Steve Easterbrook:

Dear Burger King,
Inspiration for a good cause... great idea.
We love the intention but think our two brands could do something bigger to make a difference.
We commit to raise awareness worldwide, perhaps you’ll join us in a meaningful global effort?
And every day, let's acknowledge that between us there is simply a friendly business competition and certainly not the unequaled circumstances of the real pain and suffering of war.
We’ll be in touch.
-Steve, McDonald’s CEO
P.S. A simple phone call will do next time.