Tunisia’s capital missing from book of maps, regrettably (4)

I believe the answer is:

alas

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'regrettably' is the definition.
('alas' is said before regrettable news)

I can't explain the remainder of the clue.

(Other definitions for alas that I've seen before include "Sad to say!" , "Lackaday" , "Sadly, unfortunately" , "Oh dear!" , "Regretfully!" .)

I've seen this clue in The Times.

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