Genuine monarch's leader in province (5)
I believe the answer is:
realm
'province' is the definition.
(I've seen this in another clue)
'genuine monarch's leader' is the wordplay.
'genuine' becomes 'real' (associated in meaning).
'leader' says to take the initial letters.
The initial letter of 'monarchs' is 'm'.
'real'+'m'='REALM'
'in' acts as a link.
(Other definitions for realm that I've seen before include "department" , "Dominion" , "Area of knowledge under discussion" , "Empire - state" , "where ruler holds sway?" .)