Handsome youth is behind a Spanish nobleman (6)
I believe the answer is:
adonis
'handsome youth' is the definition.
(I've seen this before)
'is behind a spanish nobleman' is the wordplay.
'behind' says to put letters next to each other.
'spanish nobleman' becomes 'don' (I've seen this before).
'a'+'don'='adon'
'is' put after 'adon' is 'ADONIS'.
(Other definitions for adonis that I've seen before include "dish" , "Handsome youth - said no (anag)" , "Aphrodite loved this beautiful youth" , "Said no to the Greek youth" , "Type of male beauty" .)