The premiere episode of 'Castle' season 8 is titled 'Brother and Sister'.Twitter/Alexi Hawley

Kate Beckett (Stana Katic) is likely to meet an important person in Richard's (Nathan Fillion) life when "Castle" returns on ABC with the premiere episode of season 8 titled "Brother and Sister".

As the title suggests, the two-part pilot sequel of popular crime drama could probably revolve around relationships and its importance in life.

Although it is not clear whether the new showrunners, Alexi Hawley and Terence Winter, are planning to introduce a sub-plot that focuses on a new relationship, the cast announcement of "Grey's Anatomy" alum Ann Cusack paves way for it.

The actress will make guest appearance in the second half of premiere episode as a "member of top-secret organisation" named Rita. The character will not just have an unexpected connection with Richard, but will also play an important role in Beckett's life with her special skills, according to TV Line.

Meanwhile, Stana Katic revealed that the first episode of ABC series will reflect on the onscreen power couple's perspective about an event. Apart from shifting the season "into a higher velocity", it will also set a base for next 20 episodes.

"Part of the exciting thing about this season is the way Alexi and Terence have envisioned the cosmic version of why the two characters (Castle and Beckett) have come together, how these roads combined. It delves into the mythology of Rick's disappearance and memory loss as well as into what inspired Beckett to become a cop in the first place," the actress told Deadline.

So it can be assumed that Cusack's character is either connected to or is responsible for the mysterious novelist's disappearance. However, "Castle" fans will have to wait for the premiere episode of season 8 titled "Brother and Sister" to know more about the sequel. It will be telecast on Monday, 21 September.

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