Ballerina not many forget dancing (6,7)
I believe the answer is:
margot fonteyn
'ballerina' is the definition.
(Margot Fonteyn was a ballerina)
'not many forget dancing' is the wordplay.
'dancing' indicates anagramming the letters.
'not'+'many'+'forget'='notmanyforget'
'notmanyforget' is an anagram of 'MARGOT FONTEYN'.
(Other definitions for margot fonteyn that I've seen before include "Dame __, English ballerina, d. 1991" , "Ballerina; not many forget (anag.)" .)