i guess years ago nazia(sultan's mom),radhaji,mohan kundra are good friends.in fact,mohan n nazia r in love with each other and radhaji too knew about it.
but nazia gets married elsewhere as per her parents wish.she was carrying mohan kundra's child,not in knowledge of anyone.
rashid,her hubby too didn't know about it n assumes the child as his own.later when he co-incidently learns about it,he abandons nazia-sultan both.
on other hand,mohan kundra goes in depression after nazia separation but radhaji comforts,consoles her n they fall in love n get married.
and rest is history...