Already mom to son Mason, 2, Kourtney Kardashian is overjoyed to be expecting a baby girl with boyfriend Scott Disick this summer.

On Sunday's premiere of Keeping Up With the Kardashians, the second-time mom-to-be, 33, can hardly hold in her excitement when she and Disick, 28, decide to reveal their new arrival's gender.

The perfect setting: Kris Jenner's family dinner, attended by Kim Kardashian, Bruce, Kendall and Kylie Jenner. "It's nice to have everybody get together and go over what's been going on in everyone's crazy-busy lives," says Disick of the Jenner matriarch's family tradition. "How else is everyone going to find out about it?"

Once she reveals her big news, Kardashian -- who confirmed her pregnancy on the cover of Us Weekly in November -- opens up about how her daughter will fit into their family.

"I am excited to have a girl, to have a new experience," says the expectant star, who's dated Disick since 2006. "I'm really excited for Mason to not have to compete with a little brother!"

As her due date nears, Kourtney has said her son quickly warmed up to the idea of being a big brother. "He's really excited," the reality star told Rachael Ray in April. "Yesterday he was talking about how he's excited to hold her and he's been like, recently obsessed with babies."

Watch more of Kourtney and Scott's big reveal in the clip above before Keeping Up With the Kardashians premieres Sunday at 9 p.m. (EST) on E!