The actor has been cast opposite the box-office draw in Sanjay Leela Bhansali's latest film Ram Leela.
A source told DNA India that Singh said: "I have never looked so good with any of my co-stars the way I will look with Kareena. She is a diva and I'm just too fortunate to be able to work with her so soon in my career.
"Kareena doesn't look anywhere the age that she is. She looks much younger than many young girls around. So that thought hasn't even crossed my mind. I'm just looking forward to having a great time working with her."
Bhansali revealed recently that he has wanted to work with Kapoor since she began her career in 2000's Refugee.
Singh, who has been praised by Shah Rukh Khan, has said that he still has a "long way to go".