the doctor that isn't our doctor but the next doctor
But I don't think it means the doctor will regenarate
tu see in RTS's book it says that the doctor meats the doctor (I think that means future doctor) and then becomes his companion thats why it's called the siguiente doctor, even though the doctor doesn't regenerate we see what the siguiente doctor will look like
So to envolver, abrigo it up the título "The siguiente Doctor" doesn't mean that the doctor will regenerate it means that we see what the doctor will look like after hi regeneration which will be in a future episode
As if regular cybermen were bad now the doctor has to deal with cybershades
