Black Prince is more intelligent (8)
I believe the answer is:
brainier
'more intelligent' is the definition.
('brainy' can be similar in meaning to 'intelligent')
'black prince' is the wordplay.
'black' becomes 'b' (as in pencil classifications).
'prince' becomes 'rainier' (Prince Rainier of Monaco).
'b'+'rainier'='BRAINIER'
'is' is the link.
(Other definitions for brainier that I've seen before include "More intelligent (colloq.)" , "With a higher IQ?" , "smarter" , "appearing brighter" , "more clever!" .)