How does Sephiroth know about the Keyblade

Who doesn't know about the Keyblade?
LOL! Seriously though, it seems as though there's been heaps of people with keyblades in the past, and I'm sure word must have gotten 'round about them sooner or later. The whole thing sounds a bit Jedi/Star Wars-y to me however. But anyways, yes, yes he does, yo(: