LEFT: From io9, "The Best Gay Wizard Action in the Potterverse" (might also like io9's Great Unsung Slash Heroes)
Q: Did Dumbledore, who believed in the prevailing power of love, ever fall in love himself?
J. K. Rowling: My truthful answer to you... I always thought of Dumbledore as gay. [ovation.] ...
Dumbledore fell in love with Grindelwald, and that that added to his horror when Grindelwald showed himself to be what he was. To an extent, do we say it excused Dumbledore a little more because falling in love can blind us to an extend, but he met someone as brilliant as he was, and rather like Bellatrix he was very drawn to this brilliant person, and horribly, terribly let down by him. Yeah, that's how I always saw Dumbledore...
To me, the most interesting part of J. K. Rowling outing Dumbledore as gay [link to BBC article, October 20, 2007,] is the way it highlights that fictional characters exist, in various ways, outside of the books they inhabit.
Rowling commented, "Oh, the fan fiction," after she made her pronouncement, referring to a flourishing industry of extramural Harry Potter-based stories.
In particular, her revelation adds possibilities to "slash" fiction.
Slash is stories fans (usually female) write about exploring the sexual possibilities between same-sex characters, usually male, who are not lovers in the original fiction, at least not explicitly.
I looked it up on Wikipedia and learned that its literary roots are in the 19th century, with erotic stories pairing Sherlock Holmes/[slash] Dr. Watson.
I first encountered slash in the 1970s.
In high school, I was hooked on reruns of the original Star Trek. In my search for even more stories, I discovered fanzines and came across a few stories involving the now-famous pairing of Kirk/Spock (K/S).
I didn't know I was witnessing the resurgence of a genre. But it wasn't prevalent in those pre-Internet days, and I soon forgot about it.
This past year, a pal told me slash has evolved since then, even including real, not fictional, people, such as certain rock stars.
I wouldn't think Dumbledore is sexy enough to elicit slash fiction. Then I remembered that Richard Harris played him in the first movies, before he died.
As I recall from Camelot, dreadful though it was, Harris was pretty attractive when he was young (left), so Dumbledore must have been too...
No doubt alert fans are already onto this.
Three minutes later:
I googled "dumbledore slash" and sure enough it has already arrived. (But Snape slash got there first. Alan Rickman...that makes sense...if someone washes Snape's hair.)
RIGHT: "Gringledore" (Dumbledore/Grindelwald) by fabledtruant, at The Great Grindeldore Appreciation Thread at Gaia Online