Former English county star making comeback (4)
I believe the answer is:
avon
'former english county' is the definition.
(I've seen this before)
'star making comeback' is the wordplay.
'star' becomes 'nova' (nova is a kind of star).
'making comeback' says the letters should be written in reverse.
'nova' back-to-front is 'AVON'.
(Other definitions for avon that I've seen before include "Bristol's river" , "Casual attitude" , "Shakespeare its swan" , "English river name in multiple use" , "Shakespeare is know as the Bard of . . . ." .)