Vocal supporter of British monarch’s terrible reign framing a century (7,6)

'vocal supporter' is the definition.
I don't know anything about this answer so I can't judge whether it can be defined by this definition.

'british monarch's terrible reign framing a century' is the wordplay.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'monarch's' becomes 'kings' (king is a kind of monarch).
'terrible' indicates an anagram.
'framing' is an insertion indicator (inserted letters are framed by the outside letters).
'century' becomes 'C' (common abbreviation).
'reign' with letters rearranged gives 'inger'.
'b'+'kings'+'inger'='bkingsinger'
'a'+'c'='ac'
'bkingsinger' placed around 'ac' is 'BACKING SINGER'.

'of' acts as a link.

Can you help me to learn more?