Remarkable reign associated with a queen (6)
I believe the answer is:
regina
'queen' is the definition.
(I've seen this before)
'remarkable reign associated with a' is the wordplay.
'remarkable' indicates anagramming the letters.
'associated with' means one lot of letters go next to another.
'reign' with letters rearranged gives 'regin'.
'regin'+'a'='REGINA'
(Other definitions for regina that I've seen before include "Queen (Latin)" , "Canadian city" , "our head of state" , "Victoria?" , "ER, Elizabeth ..." .)