Brittany Mahomes -- who this summer announced she was expecting her third child with Patrick Mahomes -- posted several shots on social media ... rockin' a cute bright orange two-piece exercise fit.

Britt, glowing, with an ever growing belly, looks great!

"Still grinding out here, " the 29-year-old said in the IG pic.

Kudos to Britt for continuing her fitness routine despite this being her "hardest" pregnancy. In August, Mahomes said this time around was rough ... saying she experienced exhaustion, sickness, and skin problems.

The silver lining ... it'll be Brittany's last pregnancy. This summer, Pat said baby three will be the last addition to the Mahomes fam.

"I'm done, I'll say that," Patrick said at Chiefs training camp this summer. "I said three and I'm done!"

Of course, Patrick and Brittany welcomed their first child, Sterling, in 2021, followed by their son Bronze in 2022.