I'm told the solver is a beast! (3)
I believe the answer is:
ewe
'beast' is the definition.
(I've seen this before)
'i'm told the solver' is the wordplay.
'i'm told' shows a homophone (sound like).
'the solver' becomes 'you' (the person solving the clue!).
'you' sounds like 'EWE'.
'is a' acts as a link.
(Other definitions for ewe that I've seen before include "Ram's partner?" , "Wool producer" , "Scottish loch" , "Source of milk" , "Farm animal" .)