This goes along with the Royal x Peasant pairing.
Two Kingdoms at war. The royal families join their soldiers on the battle field.
During a particularly brutal battle, the prince/princess of one kingdom is lost. The king/queen calls for a retreat upon the discovery. There is no time to search before hand, to retrieve a body if necessary. A search party is sent out eventually, but they find nothing. Because...
During a scavenging trip through the battlefield a young man/woman, a commoner of the opposite kingdom, finds the prince/princess near a pile of their fallen foes. The commoner is a person society has turned away from for reasons that can be discussed during the planning stages of the RP. The young man/woman takes the prince/princess away from the battlefield, their intentions not-so innocent at first. The original plan is to get the prince/princess well enough to travel, then turn them in. Things change however during the time the two characters spend together.