Crossword Genius

Series of eight wins is terrific for close relative (4,6)

Ross

I believe the answer is:

twin sister

'close relative' is the definition.
(twins are very close relatives)

'series of eight wins is terrific' is the wordplay.
'series of' indicates the answer is hidden within the clue (a series of letters from the clue).
'TWIN-SISTER' is hidden within 'eight wins is terrific'.

'for' is the link.

(Another definition for twin sister that I've seen is " Relative".)

I've seen this clue in The Times.
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