A second self (5,3)
I believe the answer is:
alter ego
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">a second self</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for alter ego that I've seen before include "A person's secondary personality" , "'One's alternative personality (5,3)'" , "Other half" , "One's secondary personality" , "'One's second self (5,3)'" .)