Stana Katic Would ‘Cry’ in Her ‘Castle’ Dressing Room Over Nathan Fillion Friction

No watercooler banter for these two. Tension between Stana Katic and Nathan Fillion on the set of Castle was so brutal that the actress broke down in tears in her dressing room, sources reveal exclusively to Us Weekly.

"Stana would cry on set because Nathan was such a bully to her," one source tells Us. A second insider adds: "Stana would go in her dressing room and cry. A lot of people who work on the show don’t like Nathan. It’s not just her."

Nathan Fillion Stana Katic
Nathan Fillion and Stana Katic in 'Castle.' Richard Cartwright/ABC

As previously reported, Katic, 37, is leaving the ABC crime procedural after eight seasons. The actress and Fillion, 45, have played onscreen couple Kate Beckett and Richard Castle on the series since its 2009 debut. And just like their characters, the costars have had their fair share of ups and downs — and were even ordered to go to counseling.

Stana Katic Nathan Fillion
Stana Katic and Nathan Fillion in 'Castle.' Richard Cartwright/ABC

"The friction was very evident," the second insider adds. "Nathan has been nasty to Stana for a long time. Stana was a pro, just wanted to get in there and do her job." (Katic's rep counters to Us that the actress "had absolutely no issues" with Fillion.)

Last year, Katic opened up about working with Fillion while attending the People's Choice Awards. "I think it all starts with [the] writing," she said of their chemistry at the time. "And after that, hopefully you are able to bounce a ball back and forth with your partner. And Nathan and I manage to bounce that ball back and forth, I think, well. I hope. People seem to like it."

Katic has yet to reveal details on her departure, but she did thank fans for their support via Twitter on Tuesday. (According to Deadline, Katic is leaving over "budgetary reasons.") Fillion hasn't spoken out about their feud either, but he did give the Canadian star a shout-out following the news.

Stana Katic
Stana Katic attends the 2016 Film Independent Spirit Awards on Feb. 27, 2016. Barry King/Getty Images

"Stana has been my partner all this time, and I thank her for creating the character Beckett who will live on for all of us as one of the greatest police officers on television," he tweeted on Tuesday. "I wish her well, and have no doubt she will succeed in everything she pursues. She will be missed."

Sign up now for the Us Weekly newsletter to get breaking celebrity news, hot pics and more delivered straight to your inbox!

Want stories like these delivered straight to your phone? Download the Us Weekly iPhone app now!