Magnificent in The Palace knocking back beer (5)

I believe the answer is:

regal

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'magnificent' is the definition.
(thesaurus)

'back beer' is the wordplay.
'back' is a reversal indicator.
'beer' becomes 'lager' (lager is a kind of beer).
'lager' reversed gives 'REGAL'.

'in the palace knocking' is the link.
This may not be right. Some or all of it may belong to another bit of the clue.

Can you help me to learn more?

(Other definitions for regal that I've seen before include "befitting a king" , "King-like" , "Grand and imposing" , "Befitting a monarch" , "Fit for a king" .)

I've seen this clue in the Irish Times.

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