Opera that’s something else (4)
I believe the answer is:
lulu
I believe this is a double definition.
'opera' is the first definition.
(opera by Alban Berg)
'something else' is the second definition.
(lulu can mean something else, something special)
'that's' is the link.
(Other definitions for lulu that I've seen before include "UK 14 7 [EURO VISION] entrant" , "wonderful thing" , "Attractive girl" , "Glaswegian 60s pop singer" , "Outstanding person or thing" .)