Burger King and McDonalds may be doing the unthinkable, and joining forces.

The two companies may be coming together to create a hybrid of their two signature burgers, and it'll be known as the "McWhopper," according to the Associated Press.

A "truce" was called by Burger King in an open letter advertisment placed in newspapers like the New York Times and the Chicago Tribune on Wednesday. If the proposal is accepted, the two companies would serve the hybrid burger at a pop-up location in Atlanta for one day only, according to the AP.

The burger would include elements of both the Whopper and the Big Mac, according to the AP. The "McWhopper" would include six ingredients from the Big Mac (including the special sauce, all-beef patty, and cheese) and six from the Whopper (including the flame-grilled patty, onion, and pickles), according to Bloomberg.

The sandwich would be sold for charity, according to Bloomberg. The proceeds from the "McWhopper" would go to a charity that promotes world peace, Peace One Day.

"Corporate activism on this scale creates mass awareness and awareness creates action and action saves lives," said Jeremy Gilley, founder of Peace One Day, according to CNBC.

McDonald's CEO Steve Easterbook commented on the proposal, calling it inspirational. However, he believes that the companies could do "something bigger to make a difference," according to the AP. There have been no confirmations of the proposal being accepted yet.