Wagner's heroine that is about to be disposed of (6)
I believe the answer is:
isolde
'wagner's heroine' is the definition.
'isolde' can be an answer for 'heroine' (I've seen this before). I am not sure about the 'wagner's' bit.
'that is about to be disposed of' is the wordplay.
'that is' becomes 'ie' (short for Latin 'id est', 'that is').
'about' is an insertion indicator.
'to be disposed of' becomes 'sold' (I've seen this before).
'ie' going around 'sold' is 'ISOLDE'.
Can you help me to learn more?
(Other definitions for isolde that I've seen before include "Tristram's lover, quite soiled" , "heroine (sic)" , "Legendary lover" , "princess of legend" , "love potion drinker" .)