UFC legend Ronda Rousey just announced she's 4 months pregnant -- and she's fired up!!!

Ronda and her husband, ex-UFC fighter Travis Browne, made the announcement in a video Wednesday morning ... saying, "Umm, how do I put this? Pow, 4 months pregnant!"

Ronda explained, "I've been pregnant since January -- so 4 months, baby bump! I can't hide it anymore so it's time to show it off."

Ronda and Travis have been talking about wanting to have children for the past few years -- she even took a hiatus from her gig with WWE back in 2019 to focus on starting a family.

Ronda said in the video there's "much more to the story" behind the pregnancy -- but didn't want to focus on those details just yet.

For the record, Ronda and Travis have NOT revealed the gender yet -- but insist they will break that news soon.

Due date -- September 22!

Ronda sent a message to her fans saying, "Thank you everybody for all the well wishes and all the positivity to get to this point."

"Baddest baby on the planet coming to you soon!"

Congrats!!!

Ronda is one of the greatest MMA fighters of all time -- she was the UFC's inaugural women's bantamweight champion and defended the belt 6 times!

Before her MMA career, she was a decorated judo athlete -- who won the bronze medal for the U.S. at the 2008 Olympics.