What do you think the consequences will be?

So I was supposed to write and give an important speech/presentation at work today to some potential clients but i completely forgot about it and only remembered that I was suppoded to be working on it for over a week when i woke up this morning so i just didn't bother to turn up for work, didn't call in sick, just did not turn up. So then my boss called me and said the clients were there everyone was in the board room waiting to hear my speech, where the hell was i? So I panicked and told him that I had been on the way to work this morning but i got abducted by a UFO and probed and stuff and the aliens must have taken the presentation before they let me go. Than I hung up before he could say anything and took the phone off the hook. I am planning on turning up to work tomorrow as though everything is normal but what do you think my boss will say when I turn up? How do you think he will react? How would you react? and what must he think of my excuse?