Revelations from SHADOWBRINGERS

[Rannie]

The wiki says he's heir apparent so I'm probably wrong about that, so I take that back.

I wouldn't go by the wiki for information much but it was mentioned in one maybe two of the cutscenes that he was named Heir to, as other have said, to stop the war of succession from occurring again. Cant remember if it was the scions (though that's who I'm leaning more towards. I could swear I remember it being said by Thancred again I could be wrong. ) that said it or it was Varis or maybe both in two different cutscenes.

[Scintilla]

I wouldn't go by the wiki for information much but it was mentioned in one maybe two of the cutscenes that he was named Heir to, as other have said, to stop the war of succession from occurring again. Cant remember if it was the scions (though that's who I'm leaning more towards. I could swear I remember it being said by Thancred again I could be wrong. ) that said it or it was Varis or maybe both in two different cutscenes.

Yes, Thancred mentions the appointment of Zenos as heir during the second 'The Call' cutscene:
"It is no coincidence that one of Varis's first acts as Emperor was to name Zenos heir apparent - family feuds being so tiresome when armies are involved. Not all welcomed his choice of successor, however."