Royal form of lager (5)
I believe the answer is:
regal
'royal' is the definition.
(I know that royal can be written as regal)
'form of lager' is the wordplay.
'form of' indicates an anagram (another form of the same letters).
'lager' is an anagram of 'REGAL'.
(Other definitions for regal that I've seen before include "Like a queen?" , "Fit for a king" , "fit for the Queen" , "King's" , "King-like" .)