Legendary bird’s goodness recalled (3)
I believe the answer is:
roc
'legendary bird's' is the definition.
(I've seen this before)
'goodness recalled' is the wordplay.
'goodness' becomes 'cor' (both are exclamations of surprise).
'recalled' says the letters should be written in reverse.
'cor' reversed gives 'ROC'.
(Other definitions for roc that I've seen before include "Arabian Nights bird" , ".Fabulous bird of the East" , "Fantastic bird" , "Vast bird of legend" , "Enormous legendary bird" .)