Turning up among ours, is unfortunately a fake (8)
I believe the answer is:
spurious
'a fake' is the definition.
(I've seen this before)
'turning up among ours is unfortunately' is the wordplay.
'turning' shows that the letters should be reversed in order.
'among' is an insertion indicator.
'unfortunately' is an anagram indicator.
'up' in reverse letter order is 'pu'.
'ours'+'is'='oursis'
'oursis' with letters rearranged gives 'srious'.
'pu' put into 'srious' is 'SPURIOUS'.
(Other definitions for spurious that I've seen before include "Inauthentic" , "Bogus" , "Plausible, but false" , "Artificial and phoney" , "Forged" .)