Not the happiest of dads set out (7)

I believe the answer is:

saddest

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'not the happiest' is the definition.
I can't tell whether this defines the answer.

'of dads set out' is the wordplay.
'of' indicates an anagram (the answer comes from or 'of' the letters).
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'dads' anagrammed gives 'sadd'.
'set' anagrammed gives 'est'.
'sadd'+'est'='SADDEST'

Can you help me to learn more?

(Other definitions for saddest that I've seen before include "Unhappiest" , "Most unhappy" , "Most doleful" , "Most gloomy" , "most dejected" .)

I've seen this clue in The Irish Independent.

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