It wouldn't be exactly shocking if another Castor clone shows up in "Orphan Black" season 4. In an interview with Buddy TV, Ari Millen, who plays the roles of every copy of Castor around, touched on the possibility of seeing another pop up.

"It's a clone show, you never know," the actor teased. "Don't be surprised, but don't get your hopes up," he went on to say. He did not elaborate more on the possibility though. Millen admits that the Castor clones are not like chalk and cheese.

Unlike the Leda clones played by Tatiana Maslany, the Castor clones do not differ from one another that much. Nonetheless, it would still be exciting to see one walking around in "Orphan Black" season 4, especially with most of the clones already dead.

Speaking of which, the actor opened up about how difficult it was filming Castor clone Seth's death. "I thought it would be a cool idea to die with my eyes open for Seth and there were multiple scenes where he was lying there dead," he recalled, describing how tough it was not to blink during scenes.

Meanwhile, Millen also revealed how hard it was to say goodbye to Rudy, who was the closest Castor clone to Mark, although he adds it was also the most fun to play. During the interview, the star teased that there's "great stuff in store" for Mark in "Orphan Black" season 4.

With the clone under the impression that he only has months to live, Mark will work to make the most out of his remaining days by spending them with Gracie. The pair, however, remains optimistic despite the nearing the demise of the lone Castor clone left.

Other spoilers regarding "Orphan Black" season 4 is the possible romance between Helena and Kristan as well as the possible return of Paul (played by Dylan Bruce) in the series.

"Orphan Black" season 4 premieres on BBC America sometime next year.