Second self (8)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">second self</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for alter ego that I've seen before include "Other half" , "'One's alternative personality (5,3)'" , "Go, relate to other self" , "Hidden or second self - in Latin" , "Mister Hyde, for example" .)