Pregnant Kourtney Kardashian had her son Mason play a special role in revealing her third baby's gender to the family -- watch a preview here. Credit: Paul Zimmerman/Getty Images

Gold star for this gender reveal! Kourtney Kardashian and Scott Disick had their son Mason, 4, play a special part in the gender reveal of their third child with their famous family.

In a new preview from Kourtney & Khloe Take the Hamptons released Dec. 2, the pregnant reality star sits with her younger sibling Khloe who congratulates the couple on the news.

"So, I heard!" Khloe says of the family news, as Disick responds: "We're having a [bleep]." (Producers teased Sunday's episode by removing any hint or confirmation of the child's sex in the preview.)

"You're not that excited?" Khloe asks the dad to Mason and Penelope, 2.

"No, I'm fine now!" Disick, 31, insists. "I'm excited."

Kourtney, 35, then explains how the adorable family moment transpired. "Mason ran in here with the [bleep] stick. There was a red star or a blue star," she recalls of the item, which indicated the child's sex. The preview then flashes back to a home video taken by Kim Kardashian from the big reveal. "We're finding out right now if Kourtney and Scott are having a boy or a girl," a makeup-free Kim says in the footage.

The eldest Kardashian daughter has been embracing her third pregnancy, even posing naked for DuJour, as revealed Tuesday, Dec. 2. "To me, nudity is not something to be ashamed of," she told the mag. "I'm at my best when I'm pregnant. It's such an amazing feeling, the transformation that your body goes through. There's something about that that's so empowering and beautiful, and I just really embrace it."

Watch the new Kourtney & Khloe Take the Hamptons clip above, and tune in on Sunday, Dec. 7, at 9 p.m. ET on E!