Groom's attendant (4,3)
I believe the answer is:
best man
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">groom's attendant</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for best man that I've seen before include "The groom's right-hand supporter" , "Bridegroom's friend" , "Bloke participating in match" , "Key union facilitator r" , "Bridegroom's mate" .)