And speaking of never giving up, the brunette beauty has admitted that she will persist in her hopes of one day marrying Cena -- despite the fact that the 39-year-old has admitted to never wanting to get tie the knot again.
In an interview with Latina magazine back in June, Bella admitted that she has "marriage fever" and regularly tries to change Cena's mind on matrimony.
"I have to remind him when I get hit on, 'I got hit on because no one saw a ring,'” she explains. "The good thing is, he's more open to marriage now -- kids, unfortunately, no."
And while the 32-year-old is open about wanting little ones, her beau's feelings on the matter aren't necessarily a dealbreaker.
"When I envision having my life without John, it hurts more than having a life without kids."
What do you think of Nikki and John's costumes? Terrifying or cute? Sound off in the comments and check out more celebrity Halloween costumes in the gallery above!
See our full breakdown of this year's costumes -- as we talk our favorites and a few we didn't care for with "Ash vs. Evil Dead" star Dana DeLorenzo -- in the video below!