Historic duchy, as standard, has a Duke (8)

I believe the answer is:

normandy

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'historic duchy' is the definition.
'normandy' can be an answer for 'duchy' (I've seen this before). I am unsure of the 'historic' bit.

'as standard has a duke' is the wordplay.
'as standard' becomes 'normy' (I can't explain this - if you can you should give a lot more credence to this answer).
'has' means one lot of letters goes inside another.
'a' becomes 'an'.
'duke' becomes 'd' (abbreviation).
'an'+'d'='and'
'normy' enclosing 'and' is 'NORMANDY'.

Can you help me to learn more?

(Other definitions for normandy that I've seen before include "9 [HOUSE]" , "North France region" , "duchy" , "Province of northern France" , "conqueror's home region" .)

I've seen this clue in The Guardian.

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