Prior to musical event duke is upset (10)
I believe the answer is:
disconcert
'upset' is the definition.
(disconcerting is a kind of upseting)
'prior to musical event duke is' is the wordplay.
'prior to' says to put letters next to each other.
'musical event' becomes 'concert' (I've seen this before**).
'duke' becomes 'd'.
'd'+'is'='dis'
'concert' put after 'dis' is 'DISCONCERT'.
(Other definitions for disconcert that I've seen before include "Disturb, unsettle" , "upset" , "Dismay" , "Throw" , "Confuse; worry" .)