User blog comment:Ninja Tank Nick/Reason I think the dragonborn Could not be emperor of Tamerial/@comment-74.75.203.235-20120329190103

The Dragonborn is NOT related to the Septim lineage. This is proven by the fact that the Dragonborn can be any race. If you understood the lore, and knew that Barenziah, a Dunmer, was pregnant with the current Emperor's child at the time, was forced to miscarriage due to the fact that she was not of Imperial blood.

Therefore, if the Emperor was to have a child with let's say, an Argonian. The mother would be forced to miscarry because it would of disrupted the Septim bloodline.

Plus Skyrim takes place 200 years after the Septim bloodline died out. The Dragonborn could not by any means be a legitimate heir to the throne. The only way for that to happen is repeat what Titus Mede I did and take the throne by conquest.