Kim Kardashian cried when her 20-year-old sister Kylie Jenner revealed she was having a baby with rapper Travis Scott, a source has revealed.

"Her first reaction was, 'Seriously?'" the source told People magazine.

"She didn't respond well at first. It's like she and Kanye [West] had gone on this whole journey to get pregnant for months, and now this happens to Kylie. She teared up. It definitely took a lot of time for her to process it."

TV personalities Kim Kardashian, Kendall Jenner and Kylie Jenner attend the 2014 MTV Video Music Awards. Photo / Getty
TV personalities Kim Kardashian, Kendall Jenner and Kylie Jenner attend the 2014 MTV Video Music Awards. Photo / Getty

Kim and rapper Kanye, who are expecting their third child through a surrogate, were initially stunned by the baby news.

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"It came out of nowhere," the source said. "It was the last thing on their radar. Kylie is just 20 and hasn't been with [boyfriend Travis] for very long. So no one saw this coming."

However, the source said Kim was "happy for Kylie" and will "support her 100 per cent, no matter what".

"But it's just a weird dynamic, after all that Kim did to intentionally have another child. It has taken a lot of time, energy and money for her to get pregnant, and now Kylie is having a baby around the same time," the source added.

One of the family's biggest worries is that Kylie's relationship with Travis is still so new.

"They don't know him too well," the source said. "They just want to make sure that this isn't a Blac Chyna situation. Kylie is so young and everybody is afraid that she could get really hurt."

Former stripper Chyna, 29, fell pregnant to Rob Kardashian after just a few months of dating. They are no longer together, but co-parent baby Dream.

Kim later hit back at the report, tweeting that it was a "fake story".

"This sounds like a very fake story," she tweeted, along with a link to a Harper's Bazaar article which quoted People magazine.

However it's not clear if she meant the pregnancy news was fake, or her supposed reaction to it.

Kylie, who is reportedly five months pregnant with a girl, has not publicly commented on the baby news.

But Caitlyn Jenner's reps yesterday confirmed the pregnancy, with a source saying the former Olympian was "shocked and disappointed".

"She thinks Kylie is way too young to have a baby, and that she should have waited until she was in a long term committed relationship," a source told Hollywood Life.

"Caitlyn is concerned that Kylie and Travis really haven't been dating very long, and that a baby will put a big strain on their relationship, but Kylie believes the opposite - that she and Travis will be together forever."

Kylie Jenner, Kim Kardashian and Kendall Jenner pose for a photo in 2007. Photo / Getty
Kylie Jenner, Kim Kardashian and Kendall Jenner pose for a photo in 2007. Photo / Getty

Kylie's mum Kris Jenner was also shocked to discover the news.

"Of course, Kris will support Kylie being a mum. But she is still adjusting to the surprise news," a source told People magazine.

"Kris is just trying to control what she can and make sure no one forgets Kylie is also a businesswoman. She wants to set Kylie Cosmetics up to sell."

Kylie began dating Travis back in April following her split from former long-term boyfriend Tyga, who has a child, son King Cairo, with Blac Chyna (Rob's ex).