The acclaimed designer duo, who have a long association with the Bachchan family, are said to be designing a special outfit for the legendary actor and are assisting in the preparations for a grand party, IANS reports.
"It is a big surprise. I can't reveal everything right now. We are designing something special for Mr Bachchan. You will get to know about everything as you get closer to the big day. Things will get clearer as we will get closer to the event," said Khosla.
The designers stated that the party is being planned by Jaya Bachchan.
"It will be Jaya Bachchan's event. We will only be helping her with all the preparations. Individually, we are not hosting any party for him," Khosla explained.
In a recent interview with Digital Spy, Abhishek Bachchan described his father's birthday as "a big day" which they would love to celebrate.
Amitabh Bachchan will turn 70 on October 11.