"The second she [North] walks into the room, Penelope gets so excited," Kourtney Kardashian said.
"We never really had cousins that were close in age … so I'm excited."
Reality TV star Kourtney said her 14-month-old daughter Penelope is "just in awe" of Kim Kardashian and Kanye West's little girl.
Kourtney's eldest child, Mason, 3, is not so sure of the Kardashian clan's latest arrival.
"I think he gets a little jealous because he and Kim were so close and so he doesn't understand because he's not the big centre of attention,” Kourtney told PEOPLE magazine.
"I don't think [Kim] knows what to do; she's just like 'You don’t like me anymore?'. She feels like he … is getting older and changing, and I think she gets confused and doesn't know how to handle it. He's like, 'Why don't you like me anymore?' cause he sees her with the baby."
The eldest of the Kardashian sisters Kourtney spoke about her baby niece at the LA premiere of Thomas & Friends: King of the Railway on Sunday.
The 34-year-old mum-of-two assured the press that her and Scott Disick's son isn't being left out.
"I give him so much attention, and he gets so much attention from everyone else that I'm like I don't even know," she said.
After Kanye West shared a photo of his first child on Kris Jenner's chatshow in August, it's easy to see why Penelope is mad about her beautiful baby cousin.
The rapper proudly showed off his tiny firstborn North West during an appearance on Kris Jenner's talk show on Friday.
The picture, which was flashed up on a giant screen, showed the adorable little girl looking at the camera with almond-shaped eyes like her famous mother . "I thought it would be cool on her grandmother's season finale to bring a picture," said Kanye.
More recently Kim and Kanye have been checking on the renovation progress at their new Bel Air mansion.
Last week the couple were spotted at the $11million residence which they toured with the team working on it. The outing was thought to be the first time they had spent time together since late August, when they met up following Kanye's appearance on Kris's chat show.