Lad twice in prison for arson (3)

I believe the answer is:

son

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'lad' is the definition.
(lad can informally mean a young boy)

'twice in prison for arson' is the wordplay.
'SON' is hidden in amongst the letters.
However, I'm unsure how the hidden word is indicated.

Can you help me to learn more?

(Other definitions for son that I've seen before include "Male scion" , "Young boy" , "Male child" , "Express paper" , "A relative" .)

I've seen this clue in the Evening Standard.

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