Duke's opening sherry in a mournful manner (8)

I believe the answer is:

doloroso

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'in a mournful manner' is the definition.
I can't tell whether this definition defines the answer.

'duke's opening sherry' is the wordplay.
'opening' indicates taking the first letters.
'sherry' becomes 'oloroso' (I've seen this before).
The first letter of 'dukes' is 'd'.
'd'+'oloroso'='DOLOROSO'

Can you help me to learn more?

(Another definition for doloroso that I've seen is " Sadly".)

I've seen this clue in The Guardian.

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