Write this type of letter for any situation in which you are communicating your appreciation to your brother or sister. You will likely need to modify this letter sample at least somewhat so that it most closely matches what you want to communicate. Include in your letter any pertinent details.
[Your letterhead, if desired; if not, your return address]
[Date of letter-month, day, and year]
[Recipient's first and last names]
[Street or P.O. box address]
[City, State ZIP code]
Dear [recipient's name]:
Where do I begin in attempting to express my deep appreciation for the caring you have shown to me as a sister? Over the years, we have grown by being close sisters, and now best friends. I appreciate so much about you and our relationship-your discerning advice, your encouragement, your humor, and so much more. I hope I am to you just as much of a support as you are to me.
Thank you again, sis. Words are not adequate to express my gratitude, but I hope you can get at least some sense of my profound appreciation.