As successor to a stern monarch (5)
I believe the answer is:
after
'as successor to a stern monarch' is the definition.
I can't tell whether this definition defines the answer.
'successor to a stern monarch' is the wordplay.
'successor to' means one lot of letters go next to another.
'a stern' becomes 'aft' (I've seen this in another clue).
'monarch' becomes 'ER' (abbreviation for Elizabeth Regina, British Queen).
'aft' put next to 'er' is 'AFTER'.
Can you help me to learn more?
(Other definitions for after that I've seen before include "Following - behind" , "Subsequently" , "In honour of" , "Coming later in time" , "Following, consequent to" .)