Auntie maybe going topless -- what joy! (7)
I believe the answer is:
elation
'what joy' is the definition.
'auntie maybe going topless' is the wordplay.
'auntie maybe' becomes 'relation'.
'going topless' means to remove the first letter.
'relation' with its first letter taken away is 'ELATION'.
(Other definitions for elation that I've seen before include "There's great joy" , "'High spirits, exhilaration (7)'" , "It's a great feeling!" , "Euphoria of toenail" , "Feeling of delight, joy" .)