Board Thread:Lore Discussion/@comment-85.74.137.231-20130605091958/@comment-7153552-20130628162340

The Dragonborn does have the blood of the dragon, and the bloodline is what caused the Amulet of Kings to work (blessed by Akatosh) and that's partly why nobody was challenging the Septims, in my opinion. Think of it like a square and rectangle; all Dragonborns have Dragonblood, but not everyone with Dragonblood is a Dragonborn.