Flash old king's formal supporter (8)

I believe the answer is:

seconder

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'formal supporter' is the definition.
'seconder' can be an answer for 'supporter' (seconder is a kind of supporter). I'm unsure of the 'formal' bit.

'flash old king's' is the wordplay.
'flash' becomes 'second' (both can mean a very short amount of time).
'old king' becomes 'ER' (abbreviation for Edward Rex, various English kings).
'second'+'er'='SECONDER'

Can you help me to learn more?

(Other definitions for seconder that I've seen before include "Supporter of a motion" , "One formally supporting" , "Person supporting" .)

I've seen this clue in The Times.

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