Guy's expression of surprise about the end of Moon River (5)
I believe the answer is:
henry
'guy's expression' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'surprise about the end of moon river' is the wordplay.
'surprise' becomes 'hey' (I can't justify this - if you can you should believe this answer much more).
'about' means one lot of letters goes inside another.
'the end of' says to take the final letters.
The last letters of 'moon river' are 'nr'.
'hey' going around 'nr' is 'HENRY'.
'of' acts as a link.
Can you help me to learn more?
(Other definitions for henry that I've seen before include "Author of The Turn of the Screw" , "Name of eight English kings" , "- Moore, sculptor" , "- the Navigator, Portuguese prince" , "CARRY ON FILM" .)