I've never read or seen GOT, but I think you should change it because
1) Your friend could recognize the name as something from GOT just by either hearing it or reading it.
2) You both write epic fantasy with dragons. That name, for a while, is "taken" associated with GOT. It's like you wouldn't use the names Jacob, Bella, and Edward, in any vampire novel/paranormal novel anytime soon. Of course, I don't know how important this name is in both your books, but I hope you see my point. (Also have never read Twilight, but I remembered the example from a blog I read long ago. Same as using Luke or Hans in a sci-fi novel.
3) I don't read epic fantasy, but from the looks of it, it seems like an unusual name that would always remind someone of a GOT tie-in. Unlike "The Palace" or "The Mountain"
4) This stuff happens all the time. Our brains see things and store them unconsciously. Then pops back up when you need a similar name. All writers experience this at one point or another. All it takes is a quick Google and a "Dang, I knew that name sounded familiar" follows after.
Oh, and welcome to AW.