Mine was transformed by a clever fellow (4,3)
I believe the answer is:
wise man
'a clever fellow' is the definition.
The answer and definition can be both people as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'mine was transformed' is the wordplay.
'transformed' is an anagram indicator.
'mine'+'was'='minewas'
'minewas' with letters rearranged gives 'WISE MAN'.
'by' is the link.
Can you help me to learn more?
(Other definitions for wise man that I've seen before include "Fellow with a gift" , "Experienced veteran" , "Sage" .)