Headdress of Spanish relative worn by a queen (5)
I believe the answer is:
tiara
'headdress' is the definition.
(tiara is a kind of headdress)
'spanish relative worn by a queen' is the wordplay.
'spanish relative' becomes 'tia' ('aunt' in Spanish).
'worn by' indicates putting letters inside (outside letters are worn by those on the inside).
'queen' becomes 'r' (abbreviation for regina, e.g. in ER ).
'a'+'r'='ar'
'tia' enclosing 'ar' is 'TIARA'.
'of' is the link.
(Other definitions for tiara that I've seen before include "Small crown" , "Decorative headband" , "Half a crown!" , "special headgear" , "Ornamental head gear" .)