Enthusiast cheers in support of popular Spanish princess (7)
I believe the answer is:
infanta
'spanish princess' is the definition.
(I've seen this before)
'enthusiast cheers in support of popular' is the wordplay.
'enthusiast' becomes 'fan' (fan is a kind of enthusiast).
'cheers' becomes 'ta' (I've seen this in other clues).
'in support of' is a charade indicator (letters next to each other) (I've seen this in other clues).
'popular' becomes 'in'.
'fan'+'ta'='fanta'
'fanta' after 'in' is 'INFANTA'.
(Other definitions for infanta that I've seen before include "Daughter of a Spanish or Portuguese king" , "noble abroad" , "Royal personage" , "European royal" , "member of the Spanish royal family" .)