The unexpected return of a familiar face caused quite a stir during the midseason finale of "Grimm" season 5, and more shocking details about the startling appearance are expected when the series returns this month.

Just like the fans, Nick (David Giuntoli) and the group were startled when they encountered a mysterious woman who looks exactly like Juliette (Bitsie Tulloch). But unlike Nick's gentle veterinarian girlfriend, the feisty character calls herself Eve, and she can ruthlessly kill her enemies.

While the previous episode did not reveal how Juliette became Eve, Tulloch shared several details about her other character in an interview with TVLine.

According to the actress, Eve had to disguise herself while she was out to finish her tasks for Hadrian's Wall so no one could recognize her.

"When Eve is out on missions, she can't run into somebody who worked with [Juliette] at the veterinary practice, or a friend, because they all think she's dead," the actress explained.

To help her with her new character, Tulloch revealed that she watched another popular TV character who had an alter ego.

"I started watching Alias over the summer, because I was like, 'All right, she's got to be incognito'. That's been really fun -- skintight leather and these awesome wigs that she wears whenever she's out."

But how will Eve's sudden appearance affect Nick and their friends in the second half of "Grimm" season 5?

According to the official synopsis for the midseason premiere episode titled "Eve of Destruction," things will be different now that Eve already revealed herself.

"Nick and the gang are still reeling from the scope of the ambush and the surprise return of "Juliette," but not everything is as it seems. In light of the heightened Wesen violence, Monroe (Silas Weir Mitchell) and Rosalee (Bree Turner) seek answers from the Wesen Council. Meanwhile, Trubel (guest star Jacqueline Toboni) has some information for Nick that will help him get what he is looking for," the synopsis reads.

The "Grimm" season 5 midseason premiere airs on Friday, Jan. 29, on NBC.