If a younger brother of the current emperor is the next heir to the Imperial Throne, he is called kotaitei (the younger brother of an Emperor who is heir apparent), and if he is a grandson of the current emperor, he is called kotaison (grandson of an Emperor who is heir apparent).
当今の弟が次期継承者である場合には、皇太弟（こうたいてい）、また当今の孫である場合は皇太孫（こうたいそん）と呼ばれる場合がある。