GK Chesterton's detective (6,5)
I believe the answer is:
father brown
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">gk chesterton's detective</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for father brown that I've seen before include "famous solver" , "Chesterton character" , "G.K. Chesterton's detective character" , "10 [SLEUTH]" .)