Just to nerd out for a second. Mayhaps the fabled holy grail is his phylactery. In which case, if we take blood to mean life which is a universally accepted relation, Brown's, and his contemporary's, "Sang Raal" or "Royal Blood" makes complete sense. Not only is the object the Holy Grail but it is also the Royal Blood, or Royal Life, of Jesus Christ. This makes Arthur and his knights not mere knights but rather Paladins. Paladins who sought to destroy the phylactery of the only lich in recorded history.