Officer of the British royal household (7)
I believe the answer is:
equerry
'officer of the british royal household' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for equerry that I've seen before include "Attendant at court" , "Personal attendant of a member of the royal family" , "Attendant at palace" , "Sovereign's officer" , "Royal aide" .)