The duo will be seen together in Vidhu Vinod Chopra's "Wazir".
"He (Amitabh Bachchan) works very hard to reinvent himself. It is not easy to do... It is a tiring process especially with each generation. To see that energy and enthusiasm is exciting. Not everybody has a career as long as him. He is inspirational to me and I focus on that aspect," Farhan told PTI.
The "Dil Chahta Hai" helmer found Big B's working style quite impressive.
"He has been here since 45 years or so he is doing films for so long and yet excited. He is still hungry for good work.
He is so enthusiastic working on sets... Working with new directors. That to me is impressive," he said.
Farhan was bowled over by the child-like quality of 73-year-old legend.
"He is a very serious person. He has a serious child like quality which comes once in a while when you are on sets.
Its really nice to see it. That excitement level, enthusiasm and energy is fun to see," he said.
"I have been an admirer of him. I have grown up watching his work. I am a fan of him. To work with him so closely so there is a feeling...of surreal. It was very enjoyable and an exciting experience.
When you begin you feel anxious then it becomes simpler," he added.
Starring Farhan Akhtar as a cop and Bachchan as a wheelchair-bound chess grandmaster, "Wazir", directed by Bejoy Nambiar, releases on January 8.
