Actual leader of my kingdom (5)
I believe the answer is:
realm
'kingdom' is the definition.
(thesaurus)
'actual leader of my' is the wordplay.
'actual' becomes 'real' ('real' can be a synonym of 'actual').
'leader of' says to take the initial letters.
The initial letter of 'my' is 'm'.
'real'+'m'='REALM'
(Other definitions for realm that I've seen before include "Monarchy" , "the UK, perhaps" , "Kingdom could be lamer" , "field of study" , "Kingdom, domain" .)