Telling lie Grant is found out (8)
I believe the answer is:
'telling' is the definition.
(relating is a kind of telling)
'lie grant is found out' is the wordplay.
'is found out' indicates an anagram (discovered out of the normal letter order).
'liegrant' with letters rearranged gives 'RELATING'.
(Other definitions for relating that I've seen before include "Telling, narrating" , "Narrating, recounting" , "account" , "Connecting things in thought or meaning" , "Rendering" .)