Celestia and Discord were the rulers of Equestria, King and Queen, and husband and wife, but there was a common misconception about the two of them. Just based off many meetings and audiences, both appeared to be very democrat and civil. They never ignited a conflict, but merely solved it with dignity and grace.
However, that never left the royal court.
Beyond royal regiments they needed to adhere to, the two were far from civil when they were with each other at times. And they. Could. Fight.
Set in "Distorted Worlds" pre-events, soon after marriage.