User blog comment:Jona19992/Third Holy Grail Hypothesis/@comment-4802891-20190408044548

As I like to stay on the surface when it comes to full speculation (because we aren't the authors), I wonder who was the Saber in this war.

If the split is lore-relevant and not just due to the Edelfelt sorcery trait, it could have been Sigurd and Siegfried, both being the same legend told in a different way, at different eras. If it isn't, it could have been anyone. We can just assume the Saber was Germanic, or at least European, and rather famous; the original summoning system had rather strict rules (that were consistantly broken but that's the point of having set rules to begin with)