I've never heard of an author outing one of her characters outside of the book's text, but J. K. Rowling just did it at Carnegie Hall!
Dumbledore is gay.
http://www.cnn.com/2007/SHOWBIZ/books/10/20/harry.potter.ap/index.html Yes, I'm clearly a Harry Potter fanatic. Don't tease.
Here is a transcribed version of Rowling's speech, in which she ties up several loose ends.
http://www.the-leaky-cauldron.org/2007/10/20/j-k-rowling-at-carnegie-hall-reveals-dumbledore-is-gay-neville-marries-hannah-abbott-and-scores-more Here is her speech in New Orleans, where she told readers what happened to Cho, Luna, and a few others.
http://blog.nola.com/living/2007/10/new_orleans_students_give_rowl.html