Board Thread:General Discussion/@comment-4411561-20140325085046/@comment-1600847-20150126202228

Another fun fact: Tiber Septim's grandson Pelagius 1st died without an heir. Tiber's niece Kintyra 1st became Empress. So 99% of the Septim dynasty is, in fact, NOT descended from Tiber, but his brother.

http://elderscrolls.wikia.com/wiki/Pelagius_I

http://elderscrolls.wikia.com/wiki/Kintyra_I