You have been invited to a party. You said you would go, but the party took place without you. You will have some explaining to do.
When you miss an important event; i.e. a social gathering or an appointment, you should apologize and offer an explanation. You should do so as soon as possible, maybe on the phone. To make it more formal, you should write to the host to apologize.
Dear Mr. and Mrs. Jones,
I am awfully sorry for not being able to attend your party last Friday despite the confirmation given to you the week before. This is due to a family misfortune.
Please accept my apology. I hope that my absence did not cause you any inconvenience.
Life and death are good excuses; for instance, somebody is taken ill or dead. However, do not make up such excuses if they are not true and please spare the gory details.
My great-aunt passed away last week, and I had to attend the funeral service. My son was suddenly taken ill.
You might not want to kill joy. If you give a general excuse, that will be acceptable as well.
I was called away on an unexpected business. Due to an unforeseen event/complication, I was unable to come. a small accident
In offering an apology, you can use these following expressions:
I am very/truly/awfully/terribly sorry for being unable to fulfil our appointment.
I apologize for ……
Please accept my apology for …….
It was totally my fault.