Kylie announced the name Friday on social media ... putting an end to constant speculation about the name of her and Travis' second child.

As we reported ... Kylie and the baby are doing great and Stormi is excited to be a big sister.

Kylie first announced she had given birth to a baby boy back on Feb. 2 ... posting a picture Sunday of what appeared to be Stormi's hand reaching out and touching her baby bro.

Remember ... news about Kylie's second pregnancy broke in August, following weeks of speculation and Internet sleuths uncovering near-daily signs that she was expecting.

Kylie officially announced she had a bun in the over not long after the toothpaste was out of the tube ... sharing a super emotional video documenting the early stages of her pregnancy, with lots of footage of Kris Jenner, Travis and Stormi.

Kendall Jenner also revealed her sis broke the news to her the OG way ... phoning her up and showing off the sonogram.

Kylie's second pregnancy was a lot more public than her first ... leaving the house more and not being too shy about showing off her baby bump.

Remember ... Kylie has said she felt pressure to give Stormi a younger sibling, and now the official Kardashian kids crew stands at 11 ... and that means Caitlyn Jenner has 19 grandkids.