Fantastic Beasts 2: 11 Major Plot Reveals From Comic-Con 2018 Trailer
6. So Much For Socks
One of a few moments of fan-service in the trailer finds Dumbledore looking into the Mirror of Erised, where we get a real answer to what he sees looking back: the floating head and torso of Gellert Grindelwald.
So much for socks, then.
A lot has been discussed about how much the movies will explore their relationship and Dumbledore's feelings for him, and while it's been stated that this film won't explicitly address Dumbledore's sexuality, the meaning here is obvious, and explains why he can't go up against Grindelwald.
It might not just be that he is in love with him, though, but that his desire - buried very, very deep - is the same control Grindelwald seeks, as they both did when they were younger. It shows the most desperate desire of a person's heart, after all, although another wrinkle is that Rowling has previously revealed he actually saw his family happily together, but for this Dumbledore his heart still belongs to Grindelwald.