Irrfan Khan reciprocated the favour done to him by Shahrukh (giving him a lead role in his home production) by doing a cameo for SRK's Red Chillies television show, Ghar Ki Baat Hai, thus dispelling all rumours that he is not very pleased by the fact that SRK is being given the prime position in the promos of Billu. In fact he is looking forward to doing more films with King Khan in future!
Irrfan is highly appreciative of Shahrukh Khan and says that the best thing about him is that even though he is at the top, he is not at all insecure. That's what makes Shahrukh different from others. And so, SRK was not afraid of giving him the plum footage, in a role which gave Irrfan a lot of scope to showcase his acting talent, while he himself played an extended cameo, as it was the demand of the script. Never once did Shahrukh try to steal Irrfan's thunder, and went out of his way to see that Irrfan's character (which is so vital to the film) was developed and highlighted properly in the film.
Well, that's what makes a confident, secure superstar!