Credit: Jason Kempin/Getty Images

When Nicole "Snooki" Polizzi broke the news of her pregnancy and engagement on the cover of Us Weekly (on stands now), fans weren't the only ones surprised by the Jersey Shore's star happy announcement.

"I actually just found out when everybody else did. That's when she decided to tell everyone," Deena Cortese, 25, said on Ryan Seacrest's KIIS-FM radio show Friday. "I think she was waiting because it's bad luck."

Indeed, Polizzi and fiance Jionni LaValle, both 24, waited until she was 15 weeks along to announce the news. "I don't care what anybody else thinks," Polizzi tells Us. "As long as I know I'm ready and he's ready."

Though Cortese was kept in the dark, she has no doubt that her MTV costar will be a "great" first-time mom. "She's a very genuine, nice person, and her heart is always in the right place. She always puts people before her. She's going to love that little meatball!"

"I think this has been her dream: getting married and having kids," Cortese added during her KIIS-FM interview. "She's really happy and I'm happy for her. I'm going to miss my little partner in crime, but I'm happy for her!"

For much more of our exclusive sit-down and photos with Snooki and her man -- why she initially lied about the pregnancy, how they found out, her cravings, how he proposed, their wedding plans and other details -- pick up the new Us Weekly, on stands now!