Disclaimer: I do not own any of these characters. They all belong to their respective studios, authors, and so forth. I just enjoy messing around with them.

After the battle, Gandalf asked Harry to join his band of merry men. Harry accepted the invitation and they went around the countryside stealing from the rich to give to the poor. However, the Dark Lord Smèagol didn't like that because he wanted his money. So he kidnapped Mr. Tumnus and they all had to go rescue him.
When Harry got there and realized it was Mr. Tumnus they were saving, he got mad and said "I'm not saving him! He's the one who drugged me with that tea."
"Don't worry. He's nice." Said Gandalf.
"Okay." Said Harry. Then they saved him.
"Thanks." Said Mr. Tumnus, after they had gotten out of the castle.
"Would you like a cup of tea, Harry?" asked Mr. Tumnus. Harry greedily accepted and drank it. When he woke up he was in another castle, but he was back in Narnia. It was the White Witch's castle. The White Witch came into the room and saw Harry. "Let's team up." She said. Harry agreed and they were off to Middle-Earth and take over.
Since time passed differently in Narnia, ten years had passed in Middle-Earth and Frodo had already destroyed the One Ring in Mount Doom after he found it in a pawn shop somewhere in Gondor (Smèagol had been down on his luck after Gandalf and the trolls stole all his money, so he had to pawn it to make his way in life). Smèagol was very bitter about losing his ring, so he asked Lord Voldemort to forge him a new one.
While Smèagol was sitting in his study one afternoon going over the stock report, the White Witch snuck up on him and said "BOO!" Smèagol got so scared that he died. Then Voldemort and the White Witch got married and this caused Harry to die of heartbreak (whether it was because of Voldemort or the White Witch, we may never know).