Dear Harry,

If you're reading this, I can only assume that you have won. If you had not, it would only make sense for you to be dead.
I can also assume that if this letter is in your possession, I was one of the casualties.
I know how you must be feeling, Harry. I need you to read this letter carefully. It's terribly important.
I want you first to know that no losses that occurred in this war were your fault. I know you feel the guilt, Harry. Understand that the people who fought in the battle did not fight it for you. They fought it for themselves, and more importantly, for the world. You were an extremely crucial part of the war, I do not deny that. But you were not the cause. This battle was inevitable. Whether it happened when it did, where it did, or elsewhere at another time. It would have happened eventually. Perhaps it is better that it happened now. Many losses would have been sustained in this fight, and if those same losses had not occurred had the battle not been when it had, then others would replace them. We won. It's over now.
This is a war, Harry. People die. Everybody went into the fight holding this knowledge, understanding it, and, most importantly, accepting it. People fought knowing that they might not live to see the end. They fought anyway. Sometimes, as much as I hate to quote Grindelwald, people have to serve the greater good.
I am so proud of you. You are every teacher's best hope for their student. How far you have come from the 13 year old boy who I taught to fight Dementors. You've grown so much. I know that Lily, James and Sirius would be just as proud as I am.
I'm sorry for perhaps not being the mentor you deserved. I've made a great deal of mistakes. As one of your father and godfather's best friends, I should have been there to guide you through your abnormally difficult life. Instead… I admit that I have had to rely on your guidance more often than I should have. I apologise for putting this weight on your shoulders- an extra weight that you certainly didn't need- and I thank you for your counsel. Especially for your advice for when it came to Dora and Ted…
And now I must request something of you, Harry. I reach out to burden you still, even from the other side! How tiresome I must seem. But this is awfully important to me.
Take care of Dora. Make sure she understands how sorry I am for all the times I have hurt her. I write this with the most desperate hopes that she has escaped the battle unscathed. I must believe this, Harry, or all will be lost.
Take care of Ted, too. You are his godfather, and he will look to you for guidance as you looked to Sirius. He has so much to learn from you. Tell him that I am sorry that I cannot be a father to him. Tell him how much I love him.
You've helped shape the world, Harry Potter. You've brought peace as you did all those years ago when you first defeated Voldemort, only this time, it is lasting. Once again I must tell you how proud I am. You've only just turned seventeen, you've only just come of age, and yet you can boast of things that fully grown men cannot. You have become braver than even I believed you could ever become, and I assure you that I believed in you from the start.
Remember me, Harry. Remember all of us, all the fatalities from this war. Do not forget us, but do not dwell on our memories. Move on. Have an ordinary life, raise a family, and keep us in your heart.

With fond memories,
Remus Lupin