K-dramas are full of bromances that vary from being rivalrous and antagonistic to almost romantic. Actor Jo In Sung and Exo-K's D.O. are the latest in the tradition of k-drama males that are the best of buddies.

The two star in "It's Okay It's Love," a comedy that's full of characters with mental issues. Some are obvious like the Tourette's syndrome that causes Lee Kwang Soo's character to blurt out sounds and words.

Other characters like Jo In Sung's Jang Jae Ryeol seem normal, even better than normal on the surface but he often sees someone who is not really there.

Jang Jae Yeol buddies around with Kang Woo, played by D.O., also known as Do Kyung Soo. The two buddy around in the drama even though Jang Jae Yeol is older than D.O.'s character Kang Woo.

And in real life Jo In Sung is also a dozen years older than his co-star.

But that has not gotten in the way of them being friends on the set of the comedy.

At a press conference for the drama, Jo In Sung talked about his co-star and their relationship.

"D.O. is probably 12 years younger than me, so it became really comfortable when I acted, thinking of him as a cute dongseng (younger brother) like that."

So the age difference does not make their relationship strange on set or off. But what has been revealed in recent episodes is that D.O.'s character does not really exist, at least not outside of Jang Jae Yeol's imagination.

That has not bothered Jo In Sung either.

""I don't think of Kang Woo too complicatedly because I can see him with my eyes," said Jo In Sung. "I just believe that Kang Woo really exists and that I have a dongseng that I share my thoughts with, and I think of D.O."

The drama about a mystery novelist, whose submerged childhood trauma leads to this particular hallucination, is D.O.'s first acting role.

Last month the singer confessed that he was a longtime fan of Jo In Sung's. He said he was so obsessed with the actor that at one point he copied Jo In Sung's haircut in the 2006 action film "A Dirty Carnival."

"I watched the film 'A Dirty Carnival' and thought Mr. Jo In Sung was incredibly awesome -- so awesome that I would even wear the same hairstyle," he said at another press conference for the drama.

It's still early in "It's Okay It's Love" but it looks as if Kang Woo may be the key to Jang Jae Ryeol's sanity.