50% off Royalist's wine (4)

I believe the answer is:

cava

I'm a little stuck... Click here to teach me more about this clue!

'wine' is the definition.
(I have seen 'Spanish wine ' mean 'cava' so perhaps 'wine' could also mean 'cava')

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for cava that I've seen before include "Spanish sparkling white wine" , "Spanish "champagne"" , "Spanish sparking wine" , "Sparkler" , "sparkling drink" .)

I've seen this clue in The Guardian.

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