Your friend bought tickets to the theatre for both of you. Write a letter to him to tell him that you cannot go to the theatre. In your letter

• Apologize
• Explain the situation
• Tell him what he can do with the extra ticket

Dear Mankeerat,

I hope this letter finds you in radiant health and the best of spirits. It is really nice of you to buy theatre tickets for both of us. Unfortunately, I shall not be able to come as my uncle and aunt have come from abroad and I have to be at home to attend to them. I sincerely apologise for the inconvenience. 

My uncle and aunt live in Canada. They arrived here three days ago with their daughter to fix her wedding with someone from my hometown. If the wedding is fixed, then all the arrangements have to be done and I am going to be very busy for the coming few days. Even now I have to be with them while they are finalizing things.

I was wondering, if you could invite our old friend Ramesh to go to the theatre with you. He is here on a holiday. He has come for the first time since he left for his higher studies in Australia two years ago. This would be your opportunity to catch up with him and your extra ticket will also not go waste. 

Hope you have a nice time with Ramesh.

Yours lovingly,
Kiran