Concerned with duke over Virginia: Queen stands by attacker (7)
I believe the answer is:
invader
'attacker' is the definition.
(I've seen this before)
'concerned with duke over virginia queen' is the wordplay.
'concerned with' becomes 'in' (I've seen this in other clues).
'duke' becomes 'd' (abbreviation).
'over' indicates putting letters inside.
'virginia' becomes 'va' (US state abbreviation).
'queen' becomes 'ER' (short for Elizabeth Regina ie Queen Elizabeth).
'in'+'d'='ind'
'ind' going around 'va' is 'invad'.
'invad'+'er'='INVADER'
'stands by' acts as a link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for invader that I've seen before include "Attacker from abroad" , "Encroacher" , "One illegally entering" , "One attacks" , "Attacker from outside" .)