User blog comment:Zippertrain85/The reasons why Serana is not from the First Era./@comment-3217145-20130510005609/@comment-9062114-20130510035835

Indeed. Harkon might've known, but not Serana, he might have actually wanted to keep his family in the dark to keep power over them. He is a devout follower of Molag Bal the Daedric Prince of Dominiation after all.