King of ancient Rome (3)
I believe the answer is:
rex
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">king of ancient rome</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 rex that I've seen before include "Part of official title of a king" , "One in the palace" , "King's title" , "Oedipus - -" , "King - Harrison?" .)