'Castle' will be back on ABC with season 8 by 21 September.Facebook/Castle

With a new cast member joining "Castle" season 8, fans are worried about the future of their favourite power couple, Richard Castle (Nathan Fillion) and Kate Beckett (Stana Katic).

Although the new showrunners--Terence Paul Winter and Alexi Hawley--are yet to reveal many details about the upcoming sequel, the lead cast members spilled out few details.

While Stana Katic described the eighth season of the crime drama as a "nail-biter", Nathan Fillion hinted on few changes that viewers can expect in the sequel.

After a discussion with the creators on season 8,  the 37-year-old actress tweeted, "Had a great mtg w @AlexiHawley & @OldManWinter14 about S8! (Nail-biter) Love #Castle cast&crew. Looking forward to playing together again."

However, the celeb refused to share any details about the sequel during a recent question and answer section with her followers on Twitter. "I don't know enough about it 2tease. Just happy @AlexiHawley & @OldManWinter14 are @ the helm & trust their vision," she posted.

Meanwhile, Fillion revealed that he is yet to meet the new cast member Toks Olagundoye, who will portray the role of security person Hayley Vargas. He even stated that the character will not bring any treat to Richard and Beckett's lives.

"In order for a show to continue and to move forward, things have to change. And things have changed, every year, for these two. Its simply just another change and its going to continue to be great. Its all part of keeping it moving forward and not boring anybody," the 44-year-old told TV Line.

ABC will premiere "Castle" season 8 on Monday, 21 September.

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