Keen local historian Jon Gunson has compiled this series entitled Friday Knight - knights who fought at the Battle of Lewes - giving each a brief biography.
I can find no evidence of de Harcourt’s presence at Lewes. For once, though, this does not matter. He was one of de Montfort’s household knights.....On May 14th, 1264, where else is he going to be? The heraldry is a bit iffy, though: a contemporary gives his coat of arms as “ Two bars”, which is of limited use. He would have carried the Harcourt shield (as above) with some kind of difference - a label, or perhaps a counterchange. He has recently made a brief appearance on television, having been Lord of Kibworth, subject of Michael Wood’s excellent series.