[Your Address Line 1]
[Your Address Line 2]
[City, Pin Code]
[Date]
My dear [Friend's Name],
I hope this letter finds you in great health and spirits. I am writing to share a very happy piece of news with you. My elder sister, [Sister's Name]'s marriage has been fixed for [Date of Marriage]. The ceremony will take place at [Venue Name], [City] at [Time].
It is a grand occasion for our family, and your presence would make it even more special. I would be delighted if you could join us for the celebrations and bless the new couple. We will have a lot of fun together.
I am eagerly looking forward to seeing you at the wedding. Please convey my regards to your parents.
Yours lovingly,
[Your Name]