Director Cameo: (Karan Johar) (plays a man talking on a cell phone behind Shahrukh Khan inside the train during film's climax.)
Ajay Devgan was the original choice for the role of Rishi, but he refused.
Kajol was initially offered the lead role in this movie, but due to scheduling conflicts, since she was already cast in Fanaa (2006), she had to refuse. She was originally going to play the role played by Rani Mukherjee, and Rani was to play the role played by Preity Zinta.
The idea of making this film struck Karan Johar while he was in London. During his trip, he saw the movie Before Sunset (2004), based on a couple who meet after parting ways. After seeing that film, he was out at a restaurant where he overheard a married couple breaking up amicably. The incident moved him and he decided to explore the idea.
India's most expensive Hindi film, reportedly made for an astronomical Rs 70 crore (~US$15 million).