Viceroy and ambassador go down following king (7)
I believe the answer is:
khedive
'viceroy' is the definition.
(thesaurus)
'ambassador go down following king' is the wordplay.
'ambassador' becomes 'he' (His or Her Excellency).
'go down' becomes 'dive' (diving is a kind of going down).
'following' is a charade indicator (letters next to each other).
'king' becomes 'k'.
'he'+'dive'='hedive'
'hedive' after 'k' is 'KHEDIVE'.
'and' acts as a link.
(Other definitions for khedive that I've seen before include "Former viceroy of Egypt" , "Old Ottoman boss" , "Egyptian viceroy" , "Turkish viceroy" .)