See Posh's partner in audience, a bearded beast (4)
I believe the answer is:
ibex
'a bearded beast' is the definition.
(ibexes are bearded goats)
'see posh's partner in audience' is the wordplay.
'see' becomes 'i' (I can't explain this - if you can you should give a lot more credence to this answer).
'posh's partner' becomes 'Becks' (David Beckham, husband of Victoria 'Posh' Beckham).
'in audience' shows a homophone (sound like).
'becks' is a homophone of 'bex'.
'i'+'bex'='IBEX'
(Other definitions for ibex that I've seen before include "Wild mountain goat" , "being nimble-footed" , "Sure-footed type" , "Sure-footed climber" , "Wild goat of North Africa" .)