A Spanish nobleman is a good-looking fellow (6)
I believe the answer is:
adonis
'a good-looking fellow' is the definition.
'adonis' can be an answer for 'fellow' (I have seen 'Handsome fellow' mean 'adonis' so perhaps 'fellow' could also mean 'adonis'). I'm not sure about the 'a good-looking' bit.
'a spanish nobleman is' is the wordplay.
'spanish nobleman' becomes 'don' (I've seen this before).
'a'+'don'+'is'='ADONIS'
Can you help me to learn more?
(Other definitions for adonis that I've seen before include "Said no to the Greek youth" , "Greek idol" , "Fit bloke" , "Handsome young man (of Greek myth)" , "striking youth" .)