Escort fellow to meet monarch, number kept back (8)
I believe the answer is:
'escort' is the definition.
(I know that chaperon is a more specific form of the action escort)
'fellow to meet monarch number kept back' is the wordplay.
'fellow' becomes 'chap' (both can mean a man).
'to meet monarch number' becomes 'nore' (I am not sure about this - if you are sure you should believe this answer much more).
'kept back' is a reversal indicator.
'nore' back-to-front is 'eron'.
Can you help me to learn more?
(Other definitions for chaperon that I've seen before include "Car-phone (anag.)" , "Person accompanying girl or younger group" , "One who accompanies and supervises" , "One accompanies the vulnerable" , "Duenna; look after" .)