How did Kabuto discover Obito’s identity before everyone else?

[Nomu]

Sure a lot of time had gone by since Obito was unmasked but Kabuto was in Izanami all the while. Did Black Zetsu tell him, did he figure it out by deduction, or did he just come late to the party while all identities were revealed?

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[minamoto]

kaboto never knew who tobi was untill he revived edomadara body...then he realized tobi wasn't madara....but tobidara laughted at kaboto's stupidity becuz he didn't knew that tobi true identity was indeed uchiha madara..

when tobi mask fell and everyone called him bobito...then kaboto must learned that through his little white snakes..