Previously-evicted houseguests from Season 21 will serve as the jury and ultimate vote to crown the winner, but before their votes are revealed live, Kirby will be shown hosting the jury roundtable and picking their brains.
"I think that the viewers will be so floored by how the votes actually shake out," Kirby toldUs Weekly, adding that all three finalists would have a strong case to make in the end.
"Trust me when I tell you that any of the three finalists can win Big Brother 21. I can't say anything other than that on this topic."
Kirby gushed, "Everyone from the casual viewer to the true Super Fan will have their jaws drop tonight."
Although the finale will air live at 9:30PM ET/PT on CBS, parts of the 90-minute episode will be pre-taped, including Kirby's segment with the jury members.
"This jury was by far, BY FAR, the best jury I've ever seen! And this is my seventh year hosting the jury roundtable discussion," he revealed.
"The main difference is that they were emotionally engaged in the discussion -- in the past we've always had at least two jurors who were affected. That wasn't the case with this group."
While Kirby acknowledged there was naturally "some groupthink occurring" in the beginning, that changed.
Kirby was referring to how either Nicole, Michie or Holly became the last jury member of the season depending on the results of the final three-part Head of Household competition.
"[The jury is] scared, and embarrassed, and feel backed into a corner... [but] once they realize that I have no agenda, then they let their guard down and get in touch with their feelings," Kirby said.
Kirby, however, told Us that he made an effort to point out when someone was bitter, even if he or she claimed not to be against a certain finalist.
"I call them out. I have to. It's my job. See, it's fine to be bitter. Just own it! I respect someone who says, 'I'm bitter and I'm going to bite emotionally!' That's not what I would personally do, but I completely understand why it occurs," Kirby shared.
But Kirby apparently doesn't even believe in a bitter jury because he believes the winner should have executed excellent jury management throughout the game.
"The right person always wins. Every. Single. Time," Kirby insisted.
"That person did what they needed to do at that exact moment in time to have his or her name called by Julie Chen Moonves more than the other person."
Kirby continued, "It really is that simple. How do the Lakers win a basketball game? They put the orange sphere though the orange netted, hoop more times than the other team. How do you win Big Brother? Have your name on more keys at the live finale."
Kirby gushed about Big Brother's 21st season being "great," and he called Nicole, Michie and Holly "a kinetic final three."
"I'm about to explode with secrets, but I'm committed to keeping everything in complete confidence... Get popcorn, put on a diaper and put the kids to bed because you'll be glued to the couch for the Big Brother 21 finale!" Kirby teased.