Opera house, the last for French city (4)
I believe the answer is:
metz
'for french city' is the definition.
(I've seen this in another clue)
'opera house the last' is the wordplay.
'opera house' becomes 'Met' (short for the Metropolitan Opera House in New York).
'the last' becomes 'Z' (Last letter alphabet).
'met'+'z'='METZ'
(Other definitions for metz that I've seen before include "Moselle River city" , "French city" , "in France" .)