Capital fellow; extremely single-minded (8)

I believe the answer is:

londoner

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'capital fellow extremely single-minded' is the definition.
I can't tell whether this definition defines the answer.

'capital fellow extremely' is the wordplay.
'capital' becomes 'london' (capital of the United Kingdom).
'fellow extremely' becomes 'er' (I am not sure about this - if you are sure you should believe this answer much more).
'london'+'er'='LONDONER'

Can you help me to learn more?

(Other definitions for londoner that I've seen before include "Possible Cockney" , "Resident of the UK capital" , "One from UK's capital" , "Capital citizen" , "city dweller" .)

I've seen this clue in The Globe and Mail.

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