The Mikaelsons finally faced their biggest enemy yet, and he happens to be one of their beloved friends. But could he really cause the vampire family's ultimate downfall in the season finale of "The Originals" season 3.

In the penultimate episode called "Give 'Em Hell Kid," Freya (Riley Voelkel) finally saw the Prophecy clearly after controlling the essence of the witch named Alexis (Stephanie Cleough). Because of that, the eldest Mikaelson sibling found out that the Beast who is said to be the one to end her life and the rest of her sibling is Marcel (Charles Michael Davis), one of their longest and most trusted ally.

Marcel began to question his loyalty to the family when he became devastated after the Mikaelsons failed to resurrect Davina (Danielle Campbell) in episode 20. This eventually turned him into the family's enemy, and even allowed Vincent (Yusuf Gatewood) to give him a serum that could help him fight the Mikaelsons.

When the original vampire siblings learned about the true meaning of the Prophecy, Elijah (Daniel Gillies) decided to kill Marcel once and for all. But Marcel already took the serum. So instead of dying, he was resurrected to become the full-fledged Beast.

In the season 3 finale, Marcel will be full of rage as he faces the Mikaelsons. In one of the trailers for the upcoming episode, titled "The Bloody Crown," Marcel furiously tells Klaus (Joseph Morgan) that he could be his equal, and refuses to accept the family's apology and believe that he can be a part of their family.

Another sneak peek shows that Marcel summons all of Klaus's biggest enemy and makes him stand trial. But it seems like Marcel has already decided to kill Klaus, until the youngest Mikaelson daughter, Rebekah (special guest star Claire Holt), returns to defend her brother. Since Rebekah and Marcel have a long history of romantic relationship, this could have an effect on the latter's actions.

The finale of "The Originals" season 3 airs on Friday, May 20, on The CW.