"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".)