Relation expressing unorthodoxy with dismissal of monarch as an aside? (13)
I believe the answer is:
parenthetical
'as an aside?' is the definition.
(something in parentheses is presented as an aside)
'relation expressing unorthodoxy with dismissal of monarch' is the wordplay.
'relation' becomes 'parent' (parent is a kind of relation).
'expressing unorthodoxy' becomes 'heretical' (heresy is unorthodoxy).
'with dismissal of' indicates named letters should be taken away.
'monarch' becomes 'ER' (abbreviation for Elizabeth Regina, British Queen).
'heretical' with 'er' taken away is 'hetical'.
'parent'+'hetical'='PARENTHETICAL'
(Other definitions for parenthetical that I've seen before include "(as this writing is)" , "Intervening" , "Qualifying" , "(Word or phrase) in brackets" , "Using brackets" .)