Ultimately Francis Scott Fitzgerald's right – excellent (7)
I believe the answer is:
stellar
'excellent' is the definition.
(I've seen this in another clue)
'ultimately francis scott fitzgerald's right' is the wordplay.
'ultimately' indicates one should take the final letters.
'fitzgerald' becomes 'Ella' (musician Ella Fitzgerald).
'right' becomes 'r' (abbreviation).
The last letters of 'francis scott' are 'st'.
'st'+'ella'+'r'='STELLAR'
(Other definitions for stellar that I've seen before include "Like highlights" , "like a star" , "celebrity" , "Excellent - shining bright?" , "Relating to the stars" .)