'Supergirl' season 3 Midseason finale spoilers: Reign, the Worldkiller challenges Supergirl [VIDEOS]

"Supergirl," starring Melissa Benoist as Kara Danvers/Supergirl, Katie McGrath as Lena Luthor, Jeremy Jordan as Winslow "Winn" Schott Jr, Mehcad Brooks as James Olsen/Guardian and Chyler Leigh as Alex Danvers, will be featured in the upcoming season 3 Winter finale episode titled "Reign." It will air in the US on Monday and in Australia on Tuesday. It will show Odette Annable (Reign/Samantha Arias) challenging Supergirl. Plus, James tries to help Lena by offering her protection.

Spoiler alert: This update contains more Season 3 'Supergirl' spoilers. Read on if you want to know about 'Reign.'

"Supergirl" season 3, episode 9 will show Kara investigating an intriguing symbol that has been appearing all over National City. According to a press release from The CW, she'll eventually discover that it's the mark of Reign, aka the leader of the Wordkillers. It is also tied to an ancient prophecy. Meanwhile, Lena will continue to experience some tension with Morgan Edge (Adrian Pasdar). This will lead James to step in and offer his protection. This gesture will also create a spark in the process. Caitlin Parrish and Paula Yoo wrote this episode, which was directed by Glen Winter.

'Reign' stars

The Internet Movie Database (IMDb) reports that Emma Tremblay (Ruby Arias), Paul Piaskowski (Seller), Patrick Rinehart (Agent 1), Briana Venskus (Agent Vasquez) and Derek Schnobb (CATCO Staff - uncredited) will appear as guest stars in this episode. They will be joined by the other members of the "Supergirl" cast including Chris Wood as Mon-El and David Harewood as J'onn J'onzz.

'Supergirl' episodes: 'Crisis on Earth-X, Part 1' and 'Legion of Super-Heroes'

The episode before "Reign" was the "Supergirl" crossover episode titled "Crisis on Earth-X, Part 1," which aired in the US on Nov. 27. It showed Supergirl teaming up with Alex and other DC multiverse characters such as Green Arrow (Stephen Amell), The Flash (Grant Gustin) and White Canary (Caity Lotz). They all had to attend Barry and Iris West's (Candice Patton) wedding. However, they were suddenly attacked by Earth-X Nazi invaders that were led by Dark Arrow and Overgirl, aka Green Arrow and Supergirl's evil doppelgangers.

These villains were also working with Prometheus and Eobard Thawne/Reverse-Flash (Tom Cavanagh). Supergirl was able to injure Overgirl, causing their enemies to retreat and regroup. Meanwhile, back at the lab, Arrow and The Flash found out that Prometheus was Tommy Merlyn (Colin Donnell). Unfortunately, he committed suicide by swallowing a pill that instantly killed him.

Aside from The Flash, Green Arrow and White Canary from "Legends of Tomorrow," Victor Garber (Dr Martin Stein), Emily Bett Rickards (Felicity Smoak), Jesse L. Martin (Joe West), Dominic Purcell (Mick Rory) Franz Drameh (Jefferson Jackson/Firestorm), Carlos Valdes (Cisco Ramon) and Keiynan Lonsdale (Wally West/Kid Flash), also made appearances in the previous episode of "Supergirl 3." "Crisis on Earth-X, Part 1," was directed by Larry Teng. The teleplay was written by Jessica Queller and Robert Rovner. Marc Guggenheim and Andrew Kreisberg wrote the story.

"Supergirl" season 3 airs on Fox 8 in Australia on Tuesdays. It airs every Monday at 8-9 pm ET/PT on The CW in the US. The next episode after "Reign" is "Legion of Super-Heroes" and it will air in the US on Jan. 15, 2018.

Watch the "Supergirl" videos below: