Twin of Artemis (6)
I believe the answer is:
apollo
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">twin of artemis</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 apollo that I've seen before include "US space flight programme, 1961-72" , "Greek god of the sun (6)" , "Greek god (twin brother of Artemis)" , "London theatre" , "Greek god of light, poetry, music, healing and prophecy" .)