Hawthorne of "The Madness of King George” (5)
I believe the answer is:
nigel
'hawthorne of the madness of king george' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for nigel that I've seen before include "Sir - - Hawthorne, actor" , "-- Gresley, railway engineer" , "Chap" , "boy" , "We all sign on (anag) -- politician" .)