What Al Green became (7)

I believe the answer is:

general

I'm a little stuck... Click here to teach me more about this clue!

'what al green became' is the definition.
I can't judge whether this definition defines the answer.

'al green became' is the wordplay.
'became' indicates an anagram (I've seen 'becomes' mean this).
'al'+'green'='algreen'
'algreen' is an anagram of 'GENERAL'.

Can you help me to learn more?

(Other definitions for general that I've seen before include "Officer of the highest rank" , "Popular" , "Officer < sweeping < public" , "blanket" , "position" .)

I've seen this clue in the Evening Standard.

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