"Everyone is thrilled for them," says a source close to the family, adding the stars have "been hoping to keep this private."
The news comes as Caitlyn Jenner seemingly spilled the beans during a campaign event. The 71-year-old reality star, who is running to replace California Gov. Gavin Newsom, mentioned she "just found out" she has another grandchild on the way.
"Eighteen grandchildren. I keep telling the girls — they're not too excited about this, but — I wanna go for 30," Caitlyn is heard saying. "Thirty grandchildren. It's a round number. I just found out the other day that I have another one in the oven. Yes, I found that out the other day. So that's 19, so we only got 10 to go."
The Olympic champion has six children, Kylie, Kendall, Brody, Brandon, Cassandra and Burt, and four stepchildren, Kourtney, Kim, Khloé and Rob. However, Page Six reports Burt is expecting his third child so that's likely who Caitlyn was referring to.
Fans have been speculating for a while now Kylie might be pregnant, but the cosmetics mogul has yet to comment publicly. A rep for Jenner didn't respond to Yahoo's request for comment.
Kylie, 24, and Scott, born Jacques Bermon Webster II, secretly welcomed Stormi Webster in February 2018. It's no surprise they are equally as hush-hush with baby no. 2.
"I'm sorry for keeping you in the dark through all the assumptions," Kylie said in an Instagram post announcing Stormi's birth. "I understand you’re used to me bringing you along on all my journeys. My pregnancy was one I chose not to do in front of the world. I knew for myself I needed to prepare for this role of a lifetime in the most positive, stress-free, and healthy way I knew how. There was no gotcha moment, no big paid reveal I had planned. I knew my baby would feel every stress and every emotion, so I chose to do it this way for my little life and our happiness."
She continued, "Pregnancy has been the most beautiful, empowering, and life-changing experience I've had in my entire life, and I’m actually going to miss it. I appreciate my friends and especially my family for helping me make this special moment as private as we could. My beautiful and healthy baby girl arrived February 1st, and I just couldn't wait to share this blessing. I've never felt love and happiness like this — I could burst! Thank you for understanding."
Kylie's has had an on-again, off-again relationship with the 30-year-old "Goosebumps" rapper in recent months, but the two are very much back together.