[She is surprised that Erica is actually asking questions, last she checked, the other girl wasn't interested in knowing things of her future. But if she's going to be around them, there are probably things she will end up finding out.]

His sister, Cora. She was-- in the vault, too. [Lydia is not a fan of the youngest Hale, but, she will keep her story as neutral as possible.]

She was poisoned with mistletoe and in order to heal her, he used his Alpha powers. It ended up being too much for him and he lost-- whatever spark that made him an Alpha.