Amazed to see fat gets beard messy (13)
I believe the answer is:
flabbergasted
'amazed' is the definition.
(synonyms)
'fat gets beard messy' is the wordplay.
'fat' becomes 'flab' (flab is a kind of fat).
'messy' is an anagram indicator.
'gets'+'beard'='getsbeard'
'getsbeard' with letters rearranged gives 'bergasted'.
'flab'+'bergasted'='FLABBERGASTED'
'to see' is the link.
(Other definitions for flabbergasted that I've seen before include "Dumbfounded" , "Gobsmacked" , "Greatly surprised" , "Thunderstruck" , "Astonished" .)