In boudoir, Henry finally prepared for Agincourt? He did (6)
I believe the answer is:
bowyer
'prepared for agincourt? he did' is the definition.
(bows were used at the Battle of Agincourt)
'in boudoir henry finally' is the wordplay.
'in' is an insertion indicator.
'boudoir' becomes 'bower'.
'finally' suggests the final letters.
The final letter of 'henry' is 'y'.
'bower' enclosing 'y' is 'BOWYER'.
(Other definitions for bowyer that I've seen before include "Weapons manufacturer" , "Robin Hood's supplier" , "one provided for the Archers?" .)