Drink was fit for royalty, on reflection (5)
I believe the answer is:
lager
'drink' is the definition.
(lager is a kind of drink)
'fit for royalty on reflection' is the wordplay.
'fit for royalty' becomes 'regal'.
'on reflection' says the letters should be written in reverse.
'regal' back-to-front is 'LAGER'.
'was' is the link.
(Other definitions for lager that I've seen before include "A brew" , "Effervescent beer" , "Pilsner, for example" , "Local offering" , "Bottom-fermented beer" .)