Dear …

RE: Absence from __(type of event)__

I regret to inform you that, I will unable to attend the __(name of event/meeting)__ that will be held on __(date)__.

Unfortunately, on that date I __(briefly describe what the situation is)__ and am required to __(briefly describe why absence is needed)__. This has been __(an unforeseen event/a difficult situation for me/a long awaited opportunity/etc.)__ and I ask for your understanding in this matter. If there was a way I could manage to be there, I would do it.

In my absence, I ask you to please keep me informed of the __(proceedings/discussions/etc)__ on __(date)__ by __(taking notes, calling me at/etc.)__. I really appreciate your cooperation and thank you once again, for your understanding of my situation.

Yours truly,