I guess he's at boarding school in Scotland per Charles, and narratively, it makes little sense to repeat that story arc, particularly when it doesn't go anywhere this time around. There's just not much to say other than his getting into Oxbridge on C/D A-levels and dropping out of the Marines (who paid for his education??) much to the chagrin of his dad (GC Marines). It may be that they just skip over him instead, and have a brief nod to a happy resolution of his sidelining in the form of the fact that his dad's title will eventually revert to him...