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 not airing a new episode this week on ABC. The next new episode, Episode 20, airs on Apr. 21. Meanwhile, Kate Beckett actress Stana Katic keeps the Caskett shippers entertained on Twitter. She also shares an update on the series finale filming schedule.

Spoiler alert: This feature contains minor spoilers and speculations on Castle Season 6. Read at your own risk.

Castle Season 6, Episode 20, titled "'That '70s Show," will feature Nathan Fillion and Stana Katic in adorable 1970s fashion. The title suggests a lot of fun, particularly in the costume department. Will this inspire Rick Castle to finalize the theme of their Caskett wedding?

In Castle Season 6, Episode 19, titled "The Greater Good," Beckett (Katic) and Castle (Fillion) come up with a shortlist of wedding invitees. It is likely going to become a private wedding with their family and NYPD colleagues.

There could be more wedding clues in the next new episode. The possibility remains for the Castle Season 6 finale to feature the Beckett-Castle nuptials. What Castle fans on Twitter now know is that production has yet to film the much-awaited finale.

"Filming 622. One more to the end of season 6! Crime-solving, coffee-toting couple killing it one shot at a time," Stana Katic tweeted, with cute toon images of Castle and Beckett. Will the wedding happen in Castle Season 6, Episode 23?

Michael Ausiello on TVLine reported the next new episode "will literally be set in '70s New York." Watch the sneak peek video on this YouTube page, or scroll down to play the clip.

Beckett and Castle are likely to be have one more confrontation with Senator William Bracken, aka the Dragon, aka the real Lazarus (Jack Coleman). It also remains possible in Castle Season 6 that viewers will see Michael Mosley again as Jerry Tyson, aka the 3XK killer. He is perceived to be dead, but his body was never found.

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

Castle Season 6, Episode 20, titled "'That '70s Show," airs on ABC on Apr. 21. Jon Polito guest stars as Harold Leone in an important mobster role.

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