That he's known to you is not any more surprising (2,8)

I believe the answer is:

no stranger

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'that he's known to you' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.

'not any more surprising' is the wordplay.
'not any' becomes 'no' (similar in meaning).
'more surprising' becomes 'stranger' (I am not sure about this - if you are sure you should believe this answer much more).
'no'+'stranger'='NO STRANGER'

'is' acts as a link.

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I've seen this clue in the Evening Standard.

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