Romantic occasion meeting duke in old hat (5)
I believe the answer is:
dated
'old hat' is the definition.
('old hat' can mean dated or old-fashioned)
'romantic occasion meeting duke' is the wordplay.
'romantic occasion' becomes 'date' (romantic meeting).
'meeting' says to put letters next to each other.
'duke' becomes 'd' (abbreviation).
'date'+'d'='DATED'
'in' acts as a link.
(Other definitions for dated that I've seen before include "Passe" , "Walked out with" , "Unfashionably old" , "Rusty" , "Pass" .)