Diya (Aishwarya Rai) is an intelligent university student with strong views on love and marriage. She spends much of her time at an orphanage in Coorg in Karnataka, helping her "Uncle" Raj Chauhan (Amitabh Bachchan) with the children living there. The story begins when Diya travels to Mumbai for her written exams. While there, she stays with her father's friend and meets their lighthearted, free-spirited son, Arjun (Vivek Oberoi). His views on love and life are completely different from hers. The pair start spending an increasing amount of time with each other and throughout all their arguments and conversations, they soon fall in love. Diya is more open about professing her feelings, while Arjun is an introvert, being reluctant and prefers not to disclose his true intentions. Diya is left feeling heartbroken after he denies loving her, and she leaves him.
Arjun travels to the orphanage, in the hopes of reconciling with Diya and apologising to her. There, he realizes his true feelings for Diya and is eager to reveal his love for her. It is revealed that Diya is now planning to marry her childhood friend, Ishaan (Suniel Shetty). Diya and Arjun start spending more time together and once again rekindle their romance. It is later revealed that Ishaan is only just a friend of Diya's and the fake marriage was a plan made up by Raj to teach Arjun the importance of always being true to love and following his heart. She then marries Arjun.
Kyun! Ho Gaya Na... marked the acting debut of Kajal Aggarwal.[2] The movie started controversy when Rai's ex-boyfriend Salman Khan allegedly threatened her then-boyfriend Oberoi.
