Princess in a Wagner opera
I believe the answer is:
isolde
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">princess in a wagner opera</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 isolde that I've seen before include "King Mark's betrothed (Wagner)" , "Tristan and . . . . . . (medieval romance)" , "princess of legend" , "Operatic heroine" , "Wagnerian heroine" .)