Prince in the mirror (4)
I believe the answer is:
emir
'prince' is the definition.
(I have seen 'Arab prince ' mean 'emir' so perhaps 'prince' could also mean 'emir')
'in the mirror' is the wordplay.
'in' says the answer is hidden in the clue.
'EMIR' can be found hidden inside 'the mirror'.
(Other definitions for emir that I've seen before include "Leading role" , "Middle-Eastern ruler" , "leader in the East" , "Top man" , "Eastern title" .)