Here we see that Catelyn Stark is in attendance… and that this must be the parlay scene in A Clash of Kings. Alas, Brienne is not carrying Renly’s banner, which would have been a good detail. From what I recall, I think it seems likely that Stannis’s banner is not carried, either.
Note the long, quilted gambeson peaking out from under Brienne’s armor, with green and gold colors that make one think of the Tyrells.
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Renly Baratheon, Catelyn Stark, Brienne of Tarth, Behind the Scenes