Man succeeding retired queen as interim ruler (6)
I believe the answer is:
regent
'interim ruler' is the definition.
(a regent rules on behalf of a monarch)
'man succeeding retired queen' is the wordplay.
'man' becomes 'gent' (gent is a kind of man).
'succeeding' means one lot of letters go next to another (succeeding can mean going after or following).
'retired' is a reversal indicator.
'queen' becomes 'ER' (abbreviation for Elizabeth Regina).
'er' backwards is 're'.
'gent' put after 're' is 'REGENT'.
'as' is the link.
(Other definitions for regent that I've seen before include "Stand-in ruler" , "Governor" , "Person who rules for a sovereign" , "Ruler during monarch's minority" , "being temporarily in charge" .)