It's the love story of two people who aren't married to each other," says music composer-turned director Vishal Bharadwaj about his new and by far most ambitious film, Mr Mehta & Mrs Singh.

While Aamir Khan [Images] was finalised as Mr Mehta a few months ago, the casting of Mrs Singh comes as a surprise.

"Kareena Kapoor [Images] is an actress I've been watching since Refugee. Her performance in Mani Ratnam's Yuva [Images] finally convinced me of her extraordinary talent," says Vishal. "After working with Shabana Azmi [Images] in Makdee and Tabu [Images] in Maqbool, I'm spoilt. I only want to work with the best actresses in the country. And you have to agree, Kareena is among our best today."

Vishal admits he approached Rani Mukerji [Images] and Preity Zinta [Images] to play the female lead. "But their dates were not matching Aamir's dates. So I had to look elsewhere. But I'm glad Kareena is in the project. Aamir has worked with Rani and Preity before but not with Kareena. This is a completely untried pairing. That adds a special edge to the on-screen romance."

Vishal seems unfazed by the drop in Aamir's equity after Mangal Pandey. "I don't think Mangal Pandey has affected Aamir's market in any way. It did stupendous business the world over. I wanted to work with Aamir for a long time. In fact, I believe some of our stars are immensely talented. Why should we hold their stardom against them?" asks Vishal.

Meanwhile, the director is getting ready for the release of The Blue Umbrella, which releases in December.

Mr Mehta & Mrs Singh will be Aamir's third release next year after Rakesh Mehra's Rang De Basanti [Images] and Kunal Kohli's film with Kajol [Images].