Lead actors of Star Plus' popular show "Yeh Rishta Kya Kehlata Hai" Karan Mehra and Hina Khan haven't been the best of friends off-screen, and now there are reports suggesting that their cold war has turned nasty.

Karan (Naitik Singhania on-screen) and Hina (Akshara Singhania on-screen) have been playing the role of husband and wife for six years now, but they do not talk off-screen. In fact, the cold war, which is very evident on the sets of the show, is showing no signs of thawing, according to reports.

Apparently, the cold war intensified when Karan did not invite his co-star Hina for the song launch of his wife Nisha Rawal. Nisha recorded AR Rahman's song "Choti Si Asha" and released it on Children's Day (14 November) to raise funds for underprivileged children.

And for the launch, Karan did not invite Hina. In fact, he did not invite any of his co-stars for the launch.

When Hina was asked about the song launch, she told 9XE.com: "So sorry, (I) have no idea about it."

Well, Karan and Hina are not the first lead pairs who cannot see eye to eye. "Diya Aur Baati Hum" leads Deepika Singh and Anas Rashid had an intense argument on the sets, and the former even slapped the latter.

"The two got into a heated argument and started abusing each other after which Deepika slapped Anas. What exactly went wrong is not clear. On screen, both play a loving married couple, but in reality they have not been on cordial terms for almost a year now," The Times of India quoted an insider as saying.