Most fashionable of stars met cast (8)
I believe the answer is:
smartest
'most fashionable' is the definition.
('smart' can be similar in meaning to 'fashionable')
'stars met cast' is the wordplay.
'cast' indicates anagramming the letters (letters are dispersed or cast around).
'stars'+'met'='starsmet'
'starsmet' is an anagram of 'SMARTEST'.
'of' is the link.
(Other definitions for smartest that I've seen before include "Most intelligent or most stylish" , "Most clever" , "Brightest or best dressed" , "Most wise" , "Cleverest; most chic" .)