Stana Katic is leaving 'Castle'
IN PHOTO: Stana Katic poses with the award she won for favorite dramatic TV actress for her role in the series "Castle" at the 2014 People's Choice Awards in Los Angeles, California January 8, 2014. REUTERS/Kevork Djansezian

"Castle" Season 6 is back with a new episode this week on ABC. Avid viewers may watch Castle 6x20 on watchabc.com. This fresh-from-hiatus instalment is titled, "That '70s Show." The Season 6 finale airs next month, and Stana Katic has already said goodbye to some co-stars in a cryptic Twitter shout-out.

Spoiler alert: This feature contains minor spoilers on Castle Season 6. Episode 20 ("That '70s Show") is the latest episode after the Mar. 24 airing of "The Greater Good."

In Castle Season 6, Episode 19, both Rick Castle (Nathan Fillion) and Kate Beckett (Stana Katic) realise that they want a private wedding. Caskett shippers remain optimistic that this wedding will be seen on or before the Season 6 finale, which is called "For Better or Worse."

However, it seems something tragic will take place in the Castle Season 6 finale. Stana Katic's teaser on Twitter has not been taken lightly. It baffles and bothers Caskett fans, particularly the supporters of the Esposito (Jon Huertas) and Ryan (Seamus Dever) "bromance."

RELATED | 'Castle' Season 6, Episode 20 Spoilers, Air Date April; Stana Katic Tweets Finale Filming Update [Watch Promo Video]

"S6 finale had us saying goodbye to a number of colleagues today. Lucky to work with these incredibly talented actors," Stana Katic tweeted a week ago. See the tweet below and pay attention to the characters in the embedded photo (Esposito and Ryan). Will the Castle Season 6 finale kill off one or more NYPD characters?

Meanwhile, there is still no official announcement on a Castle Season 7 renewal. The longer ABC takes in making a decision, the more nervous the fans get. Stana's recent tweets are much appreciated, but inevitably troubling for some fans.

"Stana it sounds like you are saying good-bye forever. Please tell me there is still hope floating!" A Stana Katic fan tweeted back. Other reactions hint of the same sentiment. Castle Season 6, Episode 20 should draw more viewers, as fans want to pick up finale clues that could be in the show.

Castle Season 6 Finale Update: Stana Katic Tweets 'Goodbye'

S6 finale had us saying goodbye to a number of colleagues today. Lucky to work with these incredibly talented actors. pic.twitter.com/UndzgJhflD

— Stana Katic (@Stana_Katic) April 8, 2014

Watch this sneak preview of Castle Season 6, Episode 20. Or play the ABC promo video below.

WATCH: Castle Season 6, Episode 20 ("That 70s Show") | ABC Promo on YouTube

Castle Season 6 airs Mondays on ABC. The next episode, "Law & Boarder," airs on Apr. 28.

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