I saw Bronn quickly looking at a white horse after the dragon attack. Dickon rides a brown horse and you can see two white horses caught in the fire as Jaime gets pushed in the water. So I think it's safe to say it was Bronn.

This is the first episode that actually feels in the same universe of BB. Less cheesy comedy, more bitterness and no improbable characters used as cheap auto references or plot devices like Tuco and the slippin' twins. I'm not liking it so far, but this episode gets an A in my book.