(I'm) (a)fraid so
A response used to politely answer a question in the affirmative when the speaker regrets that this is the case. When the phrase is abbreviated to "'fraid so," an apostrophe is sometimes used in place of the missing letter. A: "Are you really moving all the way across the country?" B: "I'm afraid so." A: "Are you going to be working late again tonight?" B: "'Fraid so."
(I'm) afraid so.and 'Fraid so.
I believe, regrettably, that the answer is yes. (The apostrophe is not always shown.) Alice: Do you have to go? John: Afraid so. Rachel: Can I expect some difficulty with Mr. Franklin? Bob: I'm afraid so.
See also: afraid