Duke on duty is removed (7)
I believe the answer is:
excised
'is removed' is the definition.
(I've seen this before)
'duke on duty' is the wordplay.
'duke' becomes 'd' (abbreviation).
'on' says to put letters next to each other.
'duty' becomes 'excise' (I've seen this in other clues).
'd' after 'excise' is 'EXCISED'.
(Other definitions for excised that I've seen before include "Taken out" , "Deleted" , "Having charges" , "Cut out, removed by cutting away" .)