Cry of joy about king visiting EU area (6)
I believe the answer is:
eureka
'cry of joy' is the definition.
(I've seen this before)
'about king visiting eu area' is the wordplay.
'about' becomes 're' (regarding**).
'king' becomes 'k'.
'visiting' is an insertion indicator.
'area' becomes 'a' (maths abbreviation).
're'+'k'='rek'
'eu'+'a'='eua'
'rek' inserted within 'eua' is 'EUREKA'.
(Other definitions for eureka that I've seen before include "Excited cry after a discovery" , "Archimedes's call of triumph" , "'I have found it!' (Greek)" , "Exclamation of triumph" , "Discoverer's triumphant cry" .)