Fans think Katic and Fillion reunion could be the greatest thing to happen to the series.
The ABC crime drama, centered on LAPD's oldest rookie, once again proved that Nathan Fillion is the main leading man of modern TV, starring in one successful show after another.
His previous series Castle was a consistent hit on ABC for 8 seasons, making Fillion the television royalty he is today.
Many fans of The Rookie began watching it just because of Fillion, so it's only natural that many of them would like to see some of the actors from Castle appear in Fillion's current show.
Of course, the number one person on this list is Stana Katic, Fillion's co-star from the TV series Castle, who played Detective Kate Beckett.
The pair of actors had amazing chemistry together and their characters echoed that perfectly, even marrying at one point. Discussing the possibility of Katic appearing in The Rookie, fans agreed that having the actress as the main villain in the series would be great. But could it really happen?
Unfortunately, this is almost impossible. After spending so many years working closely together, Fillion and Katic have fallen out badly, constantly fighting with each other.
Rumor has it that ABC even forced the actors to attend marriage counseling sessions to resolve their problems, but it probably led nowhere. The final season of Castle really proved this, as the number of scenes with Fillion and Katic together can be counted on the fingers of one hand.
If the actors can't even share one set together, how will Katic film her proposed scenes in The Rookie?
Regardless, the possibility of seeing Katic as the villain is certainly tempting, as the actress mostly plays cops rather than criminals. If only her relationship with Fillion had been great, ABC would probably have invited her to star in The Rookie much earlier, but in its current state, it's not going to happen.