The mystery surrounding Rick Castle's mysterious disappearance in "Castle" season seven still remains unanswered, but fans will finally be getting closure regarding the incident when the show's season eight returns with the premiere episode entitled "Brother and Sister."

According to The International Business Times, there is a huge chance that Kate Beckett (played by Stana Katic) will be meeting an important person in Castle's (played by Nathan Fillion) life; more particularly, she just might be meeting his sister.

It remains unclear whether or not new showrunners Alexi Hawley and Terence Winter would be creating a sub-plot for the mysterious character, who would be played by "Grey's Anatomy" alum Ann Cusack. Her character Rita is a "member of top-secret organisation," TV Line dished, adding that she would be dropping into Beckett's life "with a unique set of skills... and an unexpected connection to Castle."

The two-part pilot sequel would most certainly be dealing with relationships and how important it is to the lives of the central characters, and the first few episodes will be crucial as to how they will bring the show "into a higher velocity," and how the next 20 episodes of the season will play out.

As for Katic, she told Deadline that the reason she stayed on for "Castle" season eight is because she has faith that the new showrunners will do their characters justice.

"I started to feel the character would be safe in the next chapter of 'Castle,'" she said. "I felt confident that they knew the story, the character - Terence has been on the show since Day 1, and some of the most interesting episodes for my character were penned by Alexi - and while they are eager to shake things up and aim at telling challenging stories, they would also protect the integrity of the character."

One thing that has really gotten Katic excited about the new season is how the showrunners "envisioned the cosmic version" of why Castle and Beckett have come together, and how all roads combined have brought them together.

"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 said.

Some fans are worried that Castle and Beckett might split up this season, especially with the entry of a new character named Hayley Vargas, played by "The Neighbors" star Toks Olagundoye, but they will have to wait and see until "Castle" returns to the small screen on September 21, Monday.