Board Thread:Lore Discussion/@comment-11345660-20130908095939/@comment-3573184-20130913104524

As for when Vyrthur was turned into a vampire, I would still have to say it was around the time the Chantry was attacked.

If Vyrthur had been turned any long period of time before the chantry was attacked, I think Gelebor would have noticed his brother acting weird even back then, but his dialog suggests that Vyrthur only started acting odd around the time the Betrayed attacked, which is why he believed the Betrayed did something to him.