The rapper broke the news Thursday -- posting a photo of herself and her exposed belly on IG, and added a lengthy caption that read ... "With every ending comes a new beginning! I am so grateful to have shared this season with you, you have brought me more love, more life and most of all renewed my power! Reminded me that I can have it all!"

She adds, "You’ve reminded me that I never have to choose between life, love, and my passion! I love you so much and can not wait for you to witness what you helped me accomplish, what you pushed me to do! It’s so much easier taking life’s twists, turns and test laying down, but you, your brother and your sister have shown me why it’s worth it to push through!"

The news comes shortly after we confirmed that Cardi ran to court and filed to end her marriage with Offset. Interestingly, she doesn't mention her husband in this post ... and as a result, folks are in her comments rhetorically asking who the father might be.

Even before the divorce news -- there was already buzz that Cardi may be expecting ... in fact, we got photos of her out in NYC Wednesday where her team was trying to cover her up with umbrellas, and yes ... she did appear to be pregnant in those pics. Now we know.

This will be Cardi's third kid ... she has two other children with Offset -- Kulture and Wave.

Cardi and Offset have been on-again and off-again for a long time -- and now, it sounds like she's ready to move on from him for good ... at least that's what we've been told.

As we told you ... Cardi is seeking primary custody of their children -- and that may apply to this new baby too, assuming Offset is in fact the dad.

One thing we know for sure -- despite accusations of infidelity against Offset in the past ... we've been told that cheating was not a factor in Cardi deciding to pull the plug.