One of the Kennedy boys (3)

I believe the answer is:

ned

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'one' is the definition.
Both the definition and answer are singular nouns.
Maybe there's an association between them I don't understand?

'of the kennedy boys' is the wordplay.
'of' says the answer is hidden in the clue.
'NED' can be found hidden inside 'kennedy boys'.

Can you help me to learn more?

(Other definitions for ned that I've seen before include "rough" , "A den for Edward" .)

I've seen this clue in the Evening Standard.

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