I do not own Harry Potter and if I did, It would be nowhere near as awesome as it is.

A ten-year-old boy with jet-black hair and bright green eyes lay on the floor of the cupboard under the stairs. One might think it a strange place for a child to stay the night, but it was the only bedroom Harry Potter had known.
Harry lay on his back, listening to his aunt and uncle's house settle in the darkness. Amid the creeks and groans, an owl hooted; owls didn't usually frequent Harry's neighborhood, but this was the third night in a row that he had heard one of the birds outside of the house on Privet Drive. Harry wondered what time it was. Although he didn't have a watch, his biological clock was fairly accurate, and he judged it was about one-thirty. Sure enough, the clock in the living room struck the half-hour.
Suddenly, the house began to shake. A faint light shone from underneath the cupboard door. A male voice muttered "Lumos Maxima," and the light grew stronger. "Alohamora." Harry heard the lock unlatch and the door came open. There was a sihouette of a young man standing in the doorframe, and Harry could only make out thick round glasses and unkempt hair, both so much like his own.
"Harry," the young man said urgently. It had been this young man who had uttered those strange words. "I can't tell you who I am or how I got here, but you will find out in the future." There was a scrambling of footsteps upstairs, running towards the staircase; the Dursleys had been woken up. "I haven't much time. Take this and keep it somewhere safe. Do not open it until your eighteenth birthday." The figure tossed something at Harry, closed the door, and muttered something under his breath. Harry heard the lock catch and, from above, Uncle Vernon and Aunt Petunia's footfalls running down the staircase. When they got to the bottom, they stopped. Uncle Vernon growled. "Potter!" and at that same moment, Aunt Petunia gasped "James?" There was the sound of a whip cracking, and the light vanished. From the startled silence from his family, Harry figured that the stranger had left, too. He shoved the object, which upon later observation was found to be a gold locket, onto a shelf with the rest of his few belongings.

Eight Years Later

Harry's eighteenth birthday party had been successful. Voldemort had been dead a year, all of Harry's friends had come, Molly Weasley had baked a chocolate cake, and there had been firewhiskey. But now, at one-thirty in the morning, the feeling that he had forgotten something kept Harry awake. So he checked to see that Ginny was sleeping and went up to the attic, where he always did his thinking in the middle of the night. HE chose a box at random and began to rummage through it; it turned out to be a box of things recovered from the house at Privet Drive. Harry's hand touched cold metal and he drew out a gold locket. As it sat in his hands, the memory of that night eight years ago came flooding back to him. HE opened the locket and a folded piece of parchment fell out. There was no greeting. It simply stated:
James Potter is not your father. Actually, you know me better than you think. Yes, I am your father. For the past six months, I've been learning and experimenting with advanced time-travel spells. A month ago, I went back in time to see my parents when they were my age, but I saw your mother instead. She was gorgeous and I fell immediately in love with her. So I took some of the Polyjuice Potion I brought with me for emergency, "borrowed" some of James' hair, and disguised preceded to… "entertain" Lily. I went back several times and leaned that she was pregnant. By then, of course, she knew that I was not James and she assured me that I was the father. We vowed never to tell anyone, except you when you were ready. A week ago, I wrote this letter, put it in a locket that I had intended as a gift for Lily, and I used the last of the Polyjuice Potion and James' hair and visited you in your youth.
P.S You and I both know I'm not bright enough to think of any of this on my own; my wife helped me. I assure you she is going to punish me severely for cheating on her…

The letter ended there. Harry was shocked that James Potter was not his father and frustrated that the writer had not identified himself. Harry turned the parchment over for more information. He found it; written in very small script near the bottom of the page, was this closing:

Sorry Mate,
Ron

The End