I was halfway through my reread of the series... In AFFC...
Elder Brother was described as...
...The Elder Brother was not what Brienne had expected. He could hardly be called elder, for a start; whereas the brothers weeding in the garden had had the stooped shoulders and bent backs of old men, he stood straight and tall, and moved with the vigor of a man in the prime of his years. Nor did he have the gentle, kindly face she expected of a healer. His head was large and square, his eyes shrewd, his nose veined and red. Though he wore a tonsure, his scalp was as stubby as his heavy jaw...
so he is definitely not the one but:
...Their supper in the septry was as strange a meal as Brienne had ever eaten, though not at all unpleasant. The food was plain, but very good; there were loaves of crusty bread still warm from the ovens, crocks of fresh-churned butter, honey from the septry’s hives, and a thick stew of crabs, mussels, and at least three different kinds of fish. Septon Meribald and Ser Hyle drank the mead the brothers made, and pronounced it excellent, whilst she and Podrick contented themselves with more sweet cider. Nor was the meal a somber one. Meribald pronounced a prayer before the food was served, and whilst the brothers ate at four long trestle tables, one of their number played for them on the high harp, filling the hall with soft sweet sounds. When the Elder Brother excused the musician to take his own meal, Brother Narbert and another proctor took turns reading from The Seven-Pointed Star...
Well, what dyou guys think? could that be our dragon prince?