Man's Elgin losing his marbles (5)

I believe the answer is:

nigel

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'man's' is the definition.

'elgin losing his marbles' is the wordplay.
'elgin' can be anagrammed to 'NIGEL'.
However, I'm not sure how this is indicated.

Can you help me to learn more?

(Other definitions for nigel that I've seen before include "Chap" , "__ Mansell, 1992 F1 champion" , "-- Kennedy, violinist" , "We all sign on (anag) -- politician" , "One knighted by Conan Doyle," .)

I've seen this clue in The Sun.

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