Beyonce has been rumored to have had breast implants for a long time. The "supposed" bra size change occurred when she was relatively new to the scene. It looks like her breast size used to be a B cup, and is now a 34C. Naysayers will argue that she's not wearing a push up bra or scrunching her boobs together in any of the "before photos."
Again, Beyonce is pretty much "all natural" in before photo, and is using a clever breast size boosting technique in the after photo. Is it all smoke and mirrors, or is it actually from breast implants? This photo definitely shows the biggest bra size change. She's barely a B cup in the before picture, and is a 34C in the after.