Kareena Kapoor was the first choice of director Imtiaz Ali's
Rockstar. However, as Ranbir Kapoor had already been
finalised for the male lead, they decided against choosing Kareena,
who happens to be Ranbir's sister.
Director Imtiaz Ali, who loved Kareena Kapoor's performance in
Jab We Met wanted to cast her in Rockstar.
However, the script in Rockstar required some romantic
scenes between the romantic leads. As Ranbir and Kareena were
siblings, this would have been a problem. Moreover, the filmmakers
could not imagine replacing Ranbir with any other actor as the
character that Ranbir Kapoor plays in Rockstar was tailor
made for him. They then made a joint decision to let go of their
plan to cast Kareena in Rockstar.
In an interview with a leading newspaper, Ranbir Kapoor admitted
that Imtiaz was keen to work with Kareena but decided against doing
so as she was his (Ranbir"s) sister. Ranbir Kapoor had also said
that he wanted to work with Kareena in the future, provided the
roles were not romantic ones!