Popular Diana saucy backing the brave (8)
I believe the answer is:
intrepid
'the brave' is the definition.
(I've seen this before)
'popular diana saucy backing' is the wordplay.
'popular' becomes 'in' ('in' can mean trendy).
'diana' becomes 'Di' (Di is short for Diana).
'saucy' becomes 'pert' (synonyms).
'backing' is a reversal indicator.
'di'+'pert'='dipert'
'dipert' back-to-front is 'trepid'.
'in'+'trepid'='INTREPID'
(Other definitions for intrepid that I've seen before include "Fearlessly adventurous" , "'Brave, dauntless (8)'" , "Brave and fearless" , "Afraid not" , "without fear" .)