Last Queen sent up chief (6)
I believe the answer is:
remain
'last' is the definition.
(I've seen this before)
'queen sent up chief' is the wordplay.
'queen' becomes 'er' (abbreviation for Elizabeth Regina).
'sent up' shows that the letters should be reversed in order.
'chief' becomes 'main' (I've seen this before).
'er' reversed gives 're'.
're'+'main'='REMAIN'
(Other definitions for remain that I've seen before include "Airmen (anag.)" , "Stay around" , "Continue in position" , "Stay on when others have left" , "Stay (in position)" .)