I bought this beautiful begonia at a local nursery, and the person there had no idea what it was, and it had no tag. Actually it looks like someone propagated several of them to sell, and for ten dollars, I thought it was a good deal on the size and health. Well now the bigger leaves are starting to turn yellow and brown. I was hoping someone here can ideantify it for me and give me advise on how to care for it. Here are pics:

Whole plant-

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leaves-

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Flowers-

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Any help would be wonderful, thank you!!

-FlowerPotTipper