Happy coral is damaged? That may not be true (10)
I believe the answer is:
apocryphal
'that may not be true' is the definition.
(apocryphal means fictitious or dubious)
'happy coral is damaged?' is the wordplay.
'is damaged?' indicates an anagram.
'happy'+'coral'='happycoral'
'happycoral' with letters rearranged gives 'APOCRYPHAL'.
(Other definitions for apocryphal that I've seen before include "probably made-up" , "Fabulous" .)