I am taking this opportunity to welcome you to our family. Though, I wanted to be at your wedding to welcome you in person and extend my warm wishes to you. However, due to some urgent official work I had to go out of town and could not attend the function.
I had planned a number of things to make this day special for you and my brother but could not execute them due to this unscheduled trip. However, now that you have become a part of the family, each day would be special for us. It gives me immense pleasure to welcome you to our family and I look forward to a lot of good time together.
I would be there to meet you next week until then accept my wishes through this letter.