This letter gives a big "Doh!" when you have forgotten someone's special day.
1234, Main Street
Boston, MA 02123
07 April, 2005
<Recipient Address Goes Here>
I can't believe I forgot about <describe the occasion>! I feel like such a fool! I had it on my calendar, but things have been so hectic for me lately that the date came and went before I'd even realized it. I am so sorry for forgetting about this important occasion. You must have thought me very unkind and inconsiderate.
I hope you'll let me find a way to make it up to you. Let's go out and do something special to celebrate. Once again, I am very, very sorry!
encl: <List of enclosed items goes here>