因错过生日且未提前告知而道歉Apology for missing birthday and not notifying friend

Dear Joe, I hope you had a great birthday; anyway, the reason I am writing is to explain my absence and to apologise. To begin with, the reason for not attending your party is that my boss directed my team to work overtime to finish our latest project. This meant that we had to work very late on the night of your birthday. As to the reason I did not let you know, the project was a security software upgrade for the army and we were not permitted to make private calls. By the time we finished, I was completely exhausted and just went home and collapsed on my bed; consequently, I completely forgot to call you. I would like to express my regret as I am really so sad that I missed the celebrations. In order to do so, I want to invite you to my house next weekend to have a mini birthday party. Mark will be visiting from Spain so there is another reason to come. Please let me know if you can come, so I can plan a few surprises for you. Best wishes, John