I'm back again, girl! (4)

I believe the answer is:

mimi

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'girl' is the definition.

'i'm back again' is the wordplay.
'back' says the letters should be written backwards.
'again' becomes 'mi' (I can't justify this - if you can you should give a lot more credence to this answer).
'im' in reverse letter order is 'mi'.
'mi'+'mi'='MIMI'

Can you help me to learn more?

(Other definitions for mimi that I've seen before include "Puccini heroine" , "I'm, I'm mad about the heroine in 'La Boheme'" , "showgirl" , "Bohemian girl" , "Puccini's seamstress" .)

I've seen this clue in the Evening Standard.

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