Board Thread:General Discussion/@comment-24.157.36.219-20130614155339/@comment-9421524-20130616131135

I'm sure I had to argue this before...

The Dovahkiin (us) and the Dragonborn Emperors (Septim Bloodline) were both Dragonborns, and the Septim's may well have had a dragon soul. However, because there were no dragons for them to slay and absorb the souls of, we cannot know if they indeed had dragon souls themselves. But because the Dovahkiin has both Dragon Blood and Dragon Soul, as did Talos Stormcrown (his proper Nordic name by the way, faithless dogs) we must assume that the Dragonborn Emperors also did, but were unable to demonstrate their potential.