Al, once upset about a piano (6)

I believe the answer is:

capone

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'al' is the definition.
Both the answer and definition are singular nouns.
Maybe they are linked in a way I don't understand?

'once upset about a piano' is the wordplay.
'upset' indicates anagramming the letters.
'about' means one lot of letters goes inside another.
'piano' becomes 'p'.
'once' is an anagram of 'cone'.
'a'+'p'='ap'
'cone' placed around 'ap' is 'CAPONE'.

Can you help me to learn more?

(Other definitions for capone that I've seen before include "Al - , notorious gangster" , "US gangster (St Valentine's Day massacre)" , "Chicago gangster, d. 1947" , "Italian-American gangster, d. 1947" , "Al ..., US gangster" .)

I've seen this clue in the Evening Standard.

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