Board Thread:Lore Discussion/@comment-25291590-20130317093523/@comment-6707115-20130617114753

The Septim line does seem to have quite a few elvish empresses and mistresses, so perhaps that could have brought the line to de facto Breton. Besides, Tiber Septim's original name was Hjalti-Early Beard as Wulfharth of Atmora mentions in "The Arcturian Heresy", so at the very least Tiber Septim's father had to be a Nord. Your point on elvish and Breton interbreeding is a very good one Banneram.