RenskeSpijkerman
In Harry's fourth year, a new student (another fourth years) Renske Riddle comes to Hogwarts. She has been chosen by the goblet of fire to join the Triwizard Tournament to represent Hogwarts. Harry gets chosen as well.
Later in the story it gets clear that Renske isn't just a normal girl. She has a lot of secrets. One of them, she is the daughter of Lord Voldemort and Bellatrix Lestrange. There are rumors, because of her last name, but she doesn't tell anyone.
This is not everything happening, because Voldemort is planning to return, and that's the reason why he sent Renske to Hogwarts, but no one can find out. Because if anyone finds out, Renske will be expelled from Hogwarts and she actually is going to like it there.
Disclaimer: I don't own Harry Potter, all the rights of the original story go to J. K. Rowling. I only own my character Renske Riddle and her plot.