Ruling threesome (6)
I believe the answer is:
troika
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">ruling threesome</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 troika that I've seen before include "Team of three" , "Russian conveyance" , "Russian horse-drawn vehicle" , "Russian vehicle pulled by three horses" , "Three-horse Russian vehicle" .)