When sona was working for him he called bijoy - sir
When finally bijoy gave a nod for marriage just for sona .. but not happy with dev - he called him BABA
The day he locked up sona in office..he knew he would never need bijoy or his approval for anything .. he called him - Mr. BIJOY BOSE with full attitude
Then he came to know about soha and when soha asked to get sona's permission to go with him.. bijoy opened the door. He called him - BABA lovingly
Now again, he got sona and soha's support going against bijoys wishes .. so went back to - MR. BOSE with full attitude
So tell me aise girgit dekha kahi pe ?
I am glad sona called ishwari maa until they got separated and then switched to Mrs. dixit after there is not more rishta..