Beer from the East that's fit for a king (5)
I believe the answer is:
regal
'fit for a king' is the definition.
(I've seen this before)
'beer from the east' is the wordplay.
'beer' becomes 'lager' (lager is a kind of beer).
'from the east' shows that the letters should be reversed in order.
'lager' back-to-front is 'REGAL'.
'that's' acts as a link.
(Other definitions for regal that I've seen before include "'Majestic, royal (5)'" , "Royal - 5 down (anag)" , "Fit for a king" , "befitting a king" , "Portable organ" .)