The start and close for a refusal to invitation would be the same as in acceptance. But the body of the letter will change. It should envelop two elements, namely:
1. Expressing Regret to attend
2. Stating the Reason for Refusal.
ADVERTISEMENTS:
The letter of regret for excusing oneself is always ethically a little longer than the letter of invitation.
Letter Declining and Invite
Dear (Name),
I wish I could accept your invitation for ____________ (Days) Dinner Party. I have always enjoyed your charming hospitality and would have savored this one too! But unfortunately I am leaving for____________ (Place Name) tomorrow itself on account of the sudden illness of ____________ (Name) sister and my sister-in-law. We are very anxious about her health and I am sure you will understand why it is impossible for either of us to attend to your dinner Party next ____________ (Date).
ADVERTISEMENTS:
We are both extremely sorry to let you down/break your Heart and hope that you and ____________ (Name) will forgive us this time.
With best compliments.
Yours affectionately,
(Your Name)