In truth referring to supporter (6)

I believe the answer is:

really

'in truth' is the definition.
(synonyms)

'referring to supporter' is the wordplay.
'referring to' becomes 're'.
'supporter' becomes 'ally' (I've seen this before).
're'+'ally'='REALLY'

(Other definitions for really that I've seen before include "without a doubt" , "Indeed" , "Actually, truly" , "Well I never!" , "surprised expression" .)

I've seen this clue in The Times.

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