What is foreshadowed by Ender’s conclusion, after beating Stilson, that he is “just like Peter”?

After hurting Stilson, Ender thinks, "I am just like Peter. Take the monitor away, and I am just like Peter." This feeling remains with him throughout the book, that he will end up like his horrible older brother. Even so, the fact of his conscience seems to make him different from Peter, who displays little effort to stop himself, at least at the beginning of the book. Peter seldom shows remorse after doing the horrible things that he does. This foreshadows an act for which Ender will be completely remorseful..... something he cannot control.