Kylie made the announcement Sunday. She delivered her firstborn at Cedars-Sinai in L.A., the same hospital where sisters Kim and Kourtney delivered their broods. Rob's daughter, Dream, was also born there. Kylie's kid came out at 4:43 PM weighing 8lbs and 9 ounces.

TMZ broke the story in September that Kylie was pregnant with Travis' kid, but she's kept the pregnancy top secret. KJ never confirmed, and totally went underground ... staying out of the spotlight for the last 5 months.

We finally got a shot of her a week ago, but even then she was wearing a baggy black sweatshirt. Now the question -- how long will she keep the new baby under wraps?

Kylie addressed the secrecy in a statement, apologizing for keeping her fans in the dark.

In any event ... mazel tov!