Dear Mr. Robert Travis,
I have been sent an invitation to your wedding two weeks ago. Please accept my apologies for having replied to your letter on such a long notice. Bear in mind that I am treating your invitation as a great honor to me. And it would sadden me so much if I could not come to such a special event in your life.
This letter comes with my acceptance of your invitation. I will be coming with my wife. I hope it does not require an extra effort on your part to accommodate both of us.
I already know the details of the event from the invitation that you sent me. You can expect us to behave accordingly as a sign of respect and gratitude for the special favor you have extended us. I hope to see you soon in good health.
Allan Peter Beavis