Manservant nevertheless left Queen (6)
I believe the answer is:
butler
'manservant' is the definition.
(butler is a kind of manservant)
'nevertheless left queen' is the wordplay.
'nevertheless' becomes 'but' (I've seen this before).
'left' becomes 'l' (common abbreviation).
'queen' becomes 'er' (abbreviation for Elizabeth Regina).
'but'+'l'+'er'='BUTLER'
(Other definitions for butler that I've seen before include "Lofty head servant - what did he see?" , "Top manservant of a posh household" , "Chief male household servant" , "in charge of port?" , "Senior servant of a household" .)