I'd a son, remarkably handsome young man (6)
I believe the answer is:
adonis
'handsome young man' is the definition.
(I've seen this before)
'i'd a son remarkably' is the wordplay.
'remarkably' indicates anagramming the letters.
'id'+'a'+'son'='idason'
'idason' with letters rearranged gives 'ADONIS'.
(Other definitions for adonis that I've seen before include "Handsome youth (Gr.)" , "Beautiful Greek youth" , "No aids (anag)" , "Handsome youth - boy from Greek mythology" , "striking youth" .)