Dragon exhausted eating queen quite recently (7)
I believe the answer is:
serpent
'dragon' is the definition.
(I've seen this before)
'exhausted eating queen quite recently' is the wordplay.
I cannot quite see how this works, but
'queen' could be 'er' (short for Elizabeth Regina ie Queen Elizabeth) and 'er' is found within the answer.
'exhausted' could be 'spent' (synonyms) and 'spent' is found within the leftover letters.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for serpent that I've seen before include "Present (anag.)" , "Snake - old wind instrument" , "Eve's tempter" , "Fruit supplier" , "Instrument of the past" .)