Author Theodore seen in three German series (7)

I believe the answer is:

dreiser

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'author theodore seen' is the definition.
I don't know anything about this answer so I cannot tell whether this works.

'three german series' is the wordplay.
'three german' becomes 'drei' (I can't explain this - if you can you should give a lot more credence to this answer).
'series' becomes 'ser' (abbreviation for series).
'drei'+'ser'='DREISER'

'in' acts as a link.

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I've seen this clue in the Sydney Morning Herald.

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