The Hollow has one weakness, which will be revealed to be Hayley (Phoebe Tonkin) in episode 8 of "The Originals" season 4.

On the next episode of "The Originals" season 4, titled "Voodoo in My Blood," Hayley and Klaus (Joseph Morgan) will be visiting the ancestral world to ask for Davina's (Danielle Campbell) help in defeating The Hollow.

As seen in the episode 8 promo, Davina tells Hayley and Klaus that she is the only one who has been stopping The Hollow from killing the Mikaelsons. She also provides essential information that will help them in defeating the unknown evil entity.

"Your time is up. You need to know what you're up against. She only has one weakness. ... You. You're the one chance we have," Davina tells Hayley.

Davina's words certainly give Hayley and Klaus a shock. However, the show has yet to reveal how Hayley will become their only chance of survival under The Hollow's attack.

It is possible that it might be connected to her werewolf lineage, since Freya (Riley Voelkel) discovered that the bones of The Hollow were previously guarded by werewolves, whose bloodline unfortunately ended when Tyler Lockwood (Michael Trevino) died.

Meanwhile, "The Vampire Diaries" alum Matt Davis will cross over to "The Originals" as Alaric to bring the Mikaelsons an important artifact.

According to TVLine, this artifact is The Hollow's bone that will help the Mikaelson clan in defeating her for good. Alaric will be met by Elijah (Daniel Gillies) and Marcel (Charles Michael Davis), who will have conflict with each other brought up by past events.

While Elijah tries to take the lead and tells Marcel that they are under attack, Marcel refuses to bow down and tells him, "And I know how you handle threat." The two will be forced to work together in meeting Alaric, so they can take one step closer in defeating The Hollow.

"The Originals" season 4 airs every Friday night at 8 EDT on The CW.