Booze knocked back in Majestic (5)

I believe the answer is:

regal

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'majestic' is the definition.
(I know that majestic can be written as regal)

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for regal that I've seen before include "'Majestic, royal (5)'" , "King's" , "Kingly glare?" , "Royal - lager (anag)" , "Showing great dignity" .)

I've seen this clue in The Sun.

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