The Battle of Hastings and the crowning of William the Conqueror was in 1066 and it was then that an aristocracy that was Norman wad established.

In other words it depends on whether Hayate is one of the original companions of the Conqueror or one of their children or whether he is a Saxon knight who escaped the purge. At this point the Saxon nobles won't have acclimated to the new French court.

Also Britain was founded in 1800s when they formally unified with Scotland into one nation. And Rhiannon is Welsh which is British... now anyways (I live in Wales but am English).