Fat prince after piece of fruit (5)
I believe the answer is:
plump
'fat' is the definition.
('plump' can be a synonym of 'fat')
'prince after piece of fruit' is the wordplay.
'prince' becomes 'p'.
'after' means one lot of letters go next to another.
'piece of fruit' becomes 'plum'.
'p' after 'plum' is 'PLUMP'.
(Other definitions for plump that I've seen before include "Chubby, round" , "Well-rounded" , "Chubby, fat" , "Rather fat" , "Full of figure" .)