"Sorry to say...” (4)
'sorry to say' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for alas that I've seen before include "Lackaday" , "-- and alack!" , "Cry of woe" , "Regretfully!" , "Cry of regret" .)
(Other definitions for sadly that I've seen before include "With sorrow" , "Mournfully" , "Regrettably" , "Alas" , "I regret to say" .)