Lustful old boy returns inside, chasing queen's messenger (6,3)
I believe the answer is:
errand boy
'messenger' is the definition.
(errand boy is a kind of messenger)
'lustful old boy returns inside chasing queen's' is the wordplay.
I cannot really understand how this works, but
'old' could be 'o' (abbreviation) and 'o' is found in the answer.
'boy' could be 'rand' and 'rand' is found in the answer.
'queen' could be 'er' (abbreviation for Elizabeth Regina) and 'er' is found within the answer.
The remaining letters 'by' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for errand boy that I've seen before include "One making, eg, deliveries" , "One delivering shopkeeper's goods" , "Lad delivering messages etc" , "Young assistant" , "fag?" .)