"Sad to say . . ." (4)
'sad to say' is the definition.
('alas' is said before reporting something sad)
This is the entire clue.
(Other definitions for alas that I've seen before include "Oh dear!" , "Expression of grief/pity" , "Antipodean island state" , "Archaic exclamation of sorrow or regret" , "What a shame!" .)
(Another definition for unfortunately that I've seen is " Alas".)