"It kind of snuck up on me," Anna Paquin told PEOPLE at Tuesday's premiere of the show's seventh and final season at Hollywood's Chinese Theater.
Paquin, 31, admitted she was one of several cast members who found themselves overcome by emotions during the final script run-through, but because the show is still shooting, she had more pressing matters on her mind.
"We're still working 15 hours a day, so there's not been a lot of reflection yet," she admitted. "I'm just more worried about whether or not I will know my lines tomorrow!"
Carrie Preston's been shadowing the show's directors this season, as she plans to get behind the camera one day, and has been present for many of the actors' final scenes, but she held it together until she saw Paquin tear up.
"Once Anna started crying, I was done! Forget it!" Preston, 47, admitted. "When I see her break down, when we're acting together or in life, I just go too."
"Anna and I, we were probably the worst," Lauren Bowles admitted. "It was basically like a bunch of 12-year-old girls in a Fault in Our Stars screening. I kid you not," says the 41-year-old, who plays waitress Holly Cleary.
"I was not expecting to be so verklempt – and it was an ugly cry! There was nothing attractive about it. And I noticed a lot of the chicks weren't wearing eye makeup, but I knew all of HBO was there so I did myself up. And then I really regretted it because it was like raccoon melt."
And she may play a tough-as-coffin-nails vampire, but Kristin Bauer van Straten, 47, confessed that she was the one who kick-started the weepy chain reaction. "I'm the one that cries first – everybody knows I'm the softie," she chuckled. "And I was real solid through half the table read, and then I was a goner."
Meanwhile, Joe Manganiello, 37, insists that he didn't cry, but it seems that playing a werewolf has clearly rubbed off on him.
"This past weekend I actually went to New Orleans for the first time," he explained. "It was a full moon on Friday the 13th … and somewhere it hit me when I looked up at that moon in Louisiana. It just hit me that I'm going to be saying goodbye to this character forever. I started feeling it in my chest."