i'm just speculating here but i think that Rishaab may have been Sanjana's brother and he wants revenge for Prem rejecting her which led her to commit suicide.
had a feeling when the orignal storyline of prem and sanjana's relationship was shown that ekta may come back to this later on in the show. this may be it. why else would rishaab hate him? there is always a clue somewhere in earlier storylines for the current ones in these dramas.
what do you think?
Noshin xxx