But as Kim, 35, made an appearance at the Cannes Film Festival in France on Tuesday night (17May16), she insisted she's nothing but excited for her brother's impending fatherhood.
"I mean, it's so exciting. It's a really exciting time for him. I think he'll be the best dad. He's really just such a good, good person,” she told Entertainment Tonight.
Kim, who has two children with husband Kanye West, will also make sure she's on hand to help Rob navigate the stressful world of first time parenthood. She admitted she and her spouse have already been offering the couple advice.
"We give him - I think more me - gives him advice and it's just been a really fun time," Kim smiled. "I'm really happy for them".
Kim is the first member of the Kardashian clan to publicly comment on Rob's baby news. While she and Kylie Jenner both "liked" Rob and Blac's pregnancy announcement on Instagram, they hadn't made any statement themselves.
Kim also discussed Kylie's recent split from rapper Tyga, who has a three-year-old son King Cairo with his former partner Blac.
Asked how Kylie is doing after the break-up, Kim replied that she's "fine".
Kylie appears to be trying to move on from the end of the romance, and has been documenting her actions on Snapchat. On Monday (16May16), Kylie was being kept busy on a photoshoot where she showed off her slim frame in a bra top and wide-legged trousers. As Beyonce's new album Lemonade blasted in the background, Kylie was seen lip syncing along to the songs.
She and a friend were also seen playing volleyball on the set, before switching to a frisbee when the ball fell into the water.