IGN published an article earlier today (originally reported by Vanity Fair) in which GRRM confirmed Brienne's descended from Duncan the Tall, who of course is best known for his lifelong friendship with Aegon V, as well as his featuring in the Dunk and Egg novellas.
This happened when GRRM was at Balticon to read aloud a new chapter from his upcoming sixth book The Winds of Winter.
Can't say I'm surprised, given her impressive height and raw strength rivaling that of men.
I'd imagine Brienne's infobox would need an update as well as her storyline in the books (perhaps the series as well; though doubtful it'll be mentioned this season or even the remainder of the series).
Did you guys expect this to have been confirmed or did you find this a complete surprise?