"My twin, my fellow sassy pants, my dancing partner, my incredibly smart, beautiful, niece-y-poo, turns 3 today!" Knowles, 28, captioned. "I love her so much."
Earlier in the day, Beyonce posted a photo of Blue's Frozen-inspired birthday cake. "[Blue is] addicted to Frozen," an insider previously told Us Weekly. She "watches it several times a day" and "cries when pulled away."
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