The fighting hero in plain clothes (3)

I believe the answer is:

cid

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'the fighting hero' is the definition.
'cid' can be an answer for 'hero' (I've seen this in other clues). I'm not sure about the 'the fighting' bit.

I don't understand the rest of the clue.

Can you help me to learn more?

I've seen this clue in the Evening Standard.

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