"The drive that Katrina has is inspiring. She is there and she just doesn't stop. She has come a long way from where she started and where she is today," Ranbir said in an interview here.

"She is India's biggest actress and there is a lot of hard work, sacrifice and passion she has put behind that and I totally respect that. And the best part is that she doesn't take that for granted," the 28-year-old actor said.

Ranbir, who will be seen again with Katrina in Prakash Jha's political thriller "Rajneeti", describes Katrina as the "nicest person in the industry".

"There is an amazing positive energy about her. She is hardworking and everything she does is for the betterment of the movie. She is fun loving, passionate about cinema and passionate about her work. I share a great rapport with her," he said.

His "Ajab Prem Ki Ghazab Kahani" is slated for release Nov 6 and shows the story of a happy-go-lucky boy, who falls in love with a girl. But the girl is in love with someone else. The film also has a special appearance by Salman Khan.

Asked about his on-screen chemistry with Katrina, Ranbir said: "As far as chemistry is concerned, I always believe that chemistry never happens between two actors, it happens between two characters in the movie. It depends how the characters are written in the script and the moments and the scenes between them. That's when chemistry happens.

"Katrina and I are working for the first time, so people are finding this pairing new and fresh, but unless the film releases and unless it becomes a hit, you never know whether the chemistry has worked out or not," he said.

Ranbir, son of actors Rishi and Neetu Kapoor, made his acting debut in 2007 with Sanjay Leela's Bhansali's "Saawariya" opposite newcomer Sonam Kapoor. The film failed at the box office, but it didn't deter his growth as he received positive reviews for his performance and got good offers.

Siddharth Anand's romantic comedy "Bachna Ae Haseeno" was his second film and it hit the jackpot at the box office. And now everyone - from critics to audiences - are going ga ga over his performance in "Wake Up Sid", in which he was paired opposite Konkana Sen Sharma.

After "Ajab Prem...", Ranbir will be seen in Shimit Amin's "Rocket Singh: Salesman of The Year", "Rajneeti" and Siddharth Anand's "Anjaana Anjaani".