Unfortunately it's the Master Wizard, the Commentaries talk about the defeat of the Camoran Ursurper which happened long after Tiber Septim.

Haymon Cameron was the brother of the King of Falinesti (Might be Silvenar or Elden Root though). He usurped his brother's throne (which would explain his title of the Usurper) and embarked on his conquest of Tamriel. The mother of Mankar Cameron was, I believe, and concubine from the get-go.