The Spanish girl's boy (5)
I believe the answer is:
elvis
'boy' is the definition.
'the spanish girl's' is the wordplay.
'the spanish' becomes 'el' ('the' in Spanish).
'girl's' becomes 'Vis' (short for Violet).
'el'+'vis'='ELVIS'
(Other definitions for elvis that I've seen before include "The familiar King of rock music" , "Legendary singer" , "Singer, 1935-77" , "Mr Presley" , "The familiar R 'n'Roll king" .)