On this date in 1066, Duke William of Normandy defeated King Harold II at the Battle of Hastings. Once King Harold ceased to be a factor in British politics, having been shot through the eye with an arrow, Anglo-Saxon was demoted mainly to the tongue of an illiterate peasantry, and for decades following the Important People of England spoke Norman French (the aristocracy) or Latin (the church).
Anglo-Saxon, or Old English, had already been influenced by the Norse of the Viking invaders, and now the new overlords added their lingo to the melange. Over the next two or three centuries a new language, Middle English, emerged. It was much streamlined, as is usually the case when two language inhabit the same premises and the mistakes of adults trying to master the foreign tongue become the grammar rules of a new language.