Next week marks the beginning of the highly-anticipated crossover event between the DC shows that are on The CW. "Supergirl" goes first in the big crossover event in their eighth episode of season 3, the big event in itself called "Crisis on Earth-X."

The official synopsis of "Supergirl" season 3 episode 8 reveals that the whole gang comes together to Earth-1 to attend the wedding of Barry Allen/The Flash (Grant Gustin) to Iris West (Candice Patton). However, things go horribly wrong when the villains from Earth-X crash the ceremony.

The heroes, Supergirl (Melissa Benoist), The Flash, Green Arrow (Stephen Amell), and White Canary (Caity Lotz) lead the battle with a little help from their friends; Citizen Cold (Wentworth Miller), The Ray (Russell Tovey), Felicity Smoak (Emily Bett Rickards), Iris, and Alex (Chyler Leigh) as they try to save the world.

The trailer has been revealed for the upcoming crossover. Earth-X is the enigmatic 53rd world in the multiverse. It is the world where the Nazis emerged victorious in World War II, and all the villains are part of that army. Among the heroes in that world happens to be Citizen Cold, who joins the super team and helps them out. This crossover event might be Miller's last appearance as Captain Cold in the whole Arrowverse. So, for those who love his character, it might be a bittersweet ending.

The previous episode saw the return of Mon-El (Chris Wood) after being sent to save the Earth from the Daxamite invasion at the end of the second season. Knowing that he has been away for quite a while, Kara thought that he could never return, but fortunately he came back. Everyone, from the fans to Kara herself hoped that Mon-El coming back would bring Supergirl back to her usually cheerful self. However, it was not the case, as it brought on more questions than answers.

"Supergirl" season 3 airs Mondays at 9 p.m. EST on The CW.