King Edward perhaps, returning in mood: upset (4)
I believe the answer is:
spud
'king edward' is the definition.
(I've seen this before)
'returning in mood upset' is the wordplay.
'returning' says the letters should be written in reverse.
'in' indicates the answer is hidden within the clue.
'dups' is hidden in the letters of 'mood upset'.
'dups' backwards is 'SPUD'.
'perhaps' acts as a link.
(Other definitions for spud that I've seen before include "veg" , "Weed spade" , "Weeding spade" , "The humble colloquial potato" , "short, stocky person" .)