Gladstone's son (3)

I believe the answer is:

lad

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'son' is the definition.
(lad can mean a boy or son)

'gladstone's' is the wordplay.
'LAD' is hidden in amongst the letters.
However, I am unsure how the hidden word is indicated.

Can you help me to learn more?

(Other definitions for lad that I've seen before include "Stable employee" , "Son" , "Boy, familiar" , "(Housman's Shropshire) boy" , "Boy or youth" .)

I've seen this clue in The Mirror.

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