I don't know if you were around when ITV released the series 2 Christmas trailer....We knew from articles (since it was DA's first Christmas special the press saw the episode about a month in a special viewing before the air date) that there was a ' very moving romantic moment in the snow' and some very perceptive people could make out that it was Matthew and Mary twirling in the snow in the ITV trailer. So, if it is Charles (I don't think it is, it looks more like Gillingham to be honest, I'm not even sure it is Mary) it might not be a red herring. Like then it's hard to tell who the two people are.