Burger King is proposing -- in an open letter to the New York Times and Chicago Tribune -- a one day "ceasefire" with rival McDonald's, on September 21, which happens to be Peace Day.

In honor of Peace Day, a day of global unity recognized by the UN, Burger King suggests to McDonald's that they join forces to create the McWhopper, a combination of the Whopper and Big Mac's tastiest ingredients, "united in one delicious, peace-loving burger."

It sounds like a prank, but according to the video seen here, posted on a microsite hosting the McWhopper proposal, it really is a semi-serious suggestion, designed to raise awareness of Peace Day. Burger King has even designed a pop-up restaurant that would be situated in Atlanta (midway between McDonald's HQ in Chicago and its own in Miami) and has designed packaging and staff uniforms.

Y&R New Zealand conceived the idea, working with Burger King's other U.S. and global partners including ABPR, Code & Theory, David, Horizon, Rock Orange and Turner Duckworth. In a statement, Y&R CEO/CCO Josh Moore said the campaign is the result of an 18-month collaboration with the global Burger King marketing team. "When we first tabled this idea with Burger King we knew it was a long shot -- asking a global icon to take their hero product and blend it with that of their biggest competitor. But we've been totally overwhelmed by the enthusiasm and appetite for big thinking and bold ideas at all levels of Burger King."

However, it seems as if the McWhopper most likely will never see the light of day. McDonald's CEO Steve Easterbrook has responded with a Facebook post, in which he suggests says that the two brands could work together on something "meaningful" instead, adding "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 can only hope some other brands might get on board with Peace Day, and we can't wait to see who -- a Pepsi / Coke hybrid perhaps? Unilever collaborating with P&G?

Read more about the campaign over at AdAge.com.