The 18-year-old Keeping Up With the Kardashians star and youngest of Kim's siblings posted on her Instagram page early that morning a selfie showing her in what appears to be a bed, wearing no makeup.
Kim announced the birth of her and Kanye's baby hours later. She and the rapper, 38, are also parents to daughter North West, 2.
On Friday night, Kylie was in Miami, with A$AP Rocky, 27, and other friends.
They attended a private dinner at the Dream Hotel in the city. Kylie sat next to him and the two appeared to be flirting, a source told E! News exclusively. Her boyfriend Tyga, 26, was not spotted.
Other attendees included Hailey Baldwin, 19, and Justine Skye, 20. After the dinner, they left the hotel, while Kylie and A$AP Rocky went upstairs to the rooftop bar.
The two are friends and she is also friends with one of his crew members, a source told E! News.
They and many other celebrities, as well as Kris' boyfriend Corey Gamble, are in Miami during the Art Basel in America event, which runs until Sunday.
Watch Keeping Up With the Kardashians on Sundays at 9/8c., only on E!