Fool appearing twice in The Executioner (8)

I believe the answer is:

assassin

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'the executioner' is the definition.
(thesaurus)

'fool appearing twice in' is the wordplay.
'fool appearing' becomes 'ass' (I can't justify this - if you can you should give a lot more credence to this answer).
'twice' says to double the letters.
'ass' duplicated is 'assass'.
'assass'+'in'='ASSASSIN'

Can you help me to learn more?

(Other definitions for assassin that I've seen before include "hit man" , "Hired murderer" , "Bravo!" , "Liquidator" , "Political murderer" .)

I've seen this clue in The Sun.

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