Host current monarch (9)
I believe the answer is:
presenter
'host' is the definition.
(e.g. for a television show)
'current monarch' is the wordplay.
'current' becomes 'present' (similar in meaning).
'monarch' becomes 'er' (abbreviation for Elizabeth Regina, British Queen).
'present'+'er'='PRESENTER'
(Other definitions for presenter that I've seen before include "anchor?" , "Host of show" , "shower" , "Compere" , "Broadcast introducer" .)