Ab & Premnath question

This is plain curiosity making me start this topic.

I was just reading an article in a desi paper in US where they said that " In a recent tour of Antakshari in US,Anu Kapoor asked the people what is teh relation between actors Amitabh Bachchan and Premnath and a number of people knew the answer." But they didn't write what the relation is.

Can anyone pls tell me?