Finally, we learn truth behind the mystery of the blue eye in Harry's little mirror fragment—you know, the one that looks like Dumbledore's eye.
As it turns out, the eye belongs to Aberforth Dumbledore, brother of Albus, and he's been keeping a, well, eye on Harry (and even helping out when asked) since the remainder of the broken mirror came into his possession.
Sadly, it doesn't look like Aberforth and Albus had the greatest relationship, and so Aberforth is reluctant to help Harry along in the Horcrux:
HARRY: We need to get into Hogwarts. Tonight. Dumbledore gave us a job to do.
ABERFORTH: Did he, now? Nice job? Easy?
HARRY: We've been hunting Horcruxes. We think the last one's inside the castle, but we'll need your help getting in.
ABERFORTH: It's not a job my brother's given you, it's a suicide mission. Do yourself a favor, boy, go home. Live a little longer.
HARRY: Dumbledore trusted me to see this through.
ABERFORTH: What makes you think you can trust him? What makes you think you can believe anything my brother told you?
Yikes—Harry seems to have stepped into the middle of some serious brotherly…non-love.
Despite Aberforth's kvetching, though, he does end up helping Harry, and he does end up coming into the castle to fight alongside everyone else so Harry can complete his mission.
He must not be as jaded as he likes to make himself out to be, right? And he's Dumbledore's brother, so we know he's probably not short on bravery.