What a pathetic ending to this Illegitimate drama !! Why didn't Karan's Nani tell him the truth when Karan was harvesting such negative feelings and thoughts towards his father and opened his eyes ?
She didn't know apparently.
Kusum kept Karan away from nani so she doesn't tell him the truth (I guess after Kusum died nani came into the picture) and Kusum also left a letter with nani about Indu to give to Karan when he finds out the reality.