This is the letter Rory sent to his father in the video posted by the BBC today. I do not own Doctor Who, or this letter, or anything associated with it, I just wanted to post it on here for others to read.
Dear Dad,
This is the difficult bit. If I've got this right, you're reading this letter a week after we left in the TARDIS. The thing is, we're not coming back. We're alive and well and stuck, in New York, fifty years before I was born. We can't come home again. I won't ever see you again, and that breaks my heart. I'm so sorry, Dad. I thought about this for years and I realized there was one thing I could do. I could write to you, tell you everything. About how we lived and, despite it all, we were happy; but before we do, I need you to know. You are the best dad any son could have, and for all the times I drove you mad and you drove me mad, all the times I snapped at you. I'm sorry. I miss everything about you, especially our awkward hugs. I bought a trowel, we have a small yard, I garden; but one more important bit of business. The man whom delivered the letter, Anthony, be nice to him, cause he's your grandson. We finally adopted in 1946, Anthony Brian Williams. He can tell you everything, he'll have the family albums, and I realize having a grandson who is older than you is so far beyond weird, but I'm sorry. I love you dad. I miss you.
Love,
Rory