>>535573223
I don't remember that being written in a book, rather I remember Sarevok's horrible voice telling us outright that he wanted an offspring :
IIRC this happens when you defeat Orin as Resist Urge Durge, and then confront Sarevok about it

>You failed to bring forth issue while you helmed our cult. It is a mortal sin for a Chosen. [...] I even hoped you and my daughter might one day create a new blood-lamb for us, but it is not to be...