1. I’m sorry. I made a mistake.
2. Please accept my apologies.
3. I’m sorry. I didn’t mean to . . .
4. (I’m) sorry. I didn’t realize that . . . .
Prefacing bad news
1. I’m sorry (I have) to tell you this, but . . .
2. I hate to tell you this, but . . .
3. I don’t know how to tell you this, but . . .
4. I have some bad news.
(Formal) written apologies
1. We regret to inform you that . . .
2. Regretfully, . . .
3. Unfortunately, . . .