Capital fellow, the Italian ace! (6)
I believe the answer is:
manila
'capital' is the definition.
(Manila is an example)
'fellow the italian ace' is the wordplay.
'fellow' becomes 'man' (I've seen this before).
'the italian' becomes 'il' (the in Italian).
'ace' becomes 'a'.
'man'+'il'+'a'='MANILA'
(Other definitions for manila that I've seen before include "Strong brown paper; cigar, cheroot" , "Brown paper and Philippine city" , "Island capital" , "Nail Ma up with strong paper" , "Capital of Philippines" .)