Excuse me, but...
I am terribly sorry but,
I'm sorry to trouble you, but …; Excuse me, but ….
I'm afraid ~.
A thousand apologies.
to be faultless―perfect―ideal―satisfactory―unexceptionable―unimpeachable―above reproach―all that one can desire―all that can be desired―everything a person or thing should be―as it should be―to leave nothing to be desired
I am sorry to say―I regret to say―to my regret.
も少し