a well-mannered fellow, extremely ideal, being nobility formerly (10)

'nobility formerly' is the definition.
I can't judge whether this definition defines the answer.

'a well-mannered fellow extremely ideal being' is the wordplay.
'a well-mannered fellow' becomes 'gent' (I've seen this in another clue).
'extremely' suggests removing the centre (only the extremes of the word are used).
'being' becomes 'esse' (philosophical term for being or existence).
'ideal' with its centre removed is 'il'.
'gent'+'il'+'esse'='GENTILESSE'

Can you help me to learn more?