Boy’s other name is Don Juan (6,3)
I believe the answer is:
ladies man
'don juan' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.
'boy's other name is' is the wordplay.
'boy' becomes 'lad' (lad is a kind of boy).
'other' indicates an anagram.
'name'+'is'='nameis'
'nameis' is an anagram of 'iesman'.
'lad'+'iesman'='LADIES' MAN'
Can you help me to learn more?
(Other definitions for ladies man that I've seen before include "Libertine" , "His philandering" , "Would-be seducer" , "Playboy" , "(Would be) seducer of women?" .)