The eldest Kardashian sister posted new photos of her belly Sunday -- this after letting the world (and her husband) know that she was newly expecting in awesome fashion. As it turns out, it appears she's quite far along ... meaning she's been sitting on this for a minute.

We're not gonna play doctor and pretend we know where she's at in the pregnancy -- but at first glance, it would seem she's well into the first trimester ... and then some, perhaps.

As for the pics themselves ... they're absolutely adorable. You see Kourt and Trav hugging up on each other -- smooching, hugging, and even a little drumming (kidding, of course) with TB playfully using his sticks on her stomach. The dude even goes in to kiss the baby-to-be.

It's interesting ... we know for a fact Travis was completely stunned to learn that Kourtney was pregnant -- based on his reaction to the announcement, which went down live during a Blink-182 concert. As we all know ... KK blasted the news out via old-school signage.

However, considering how preggo she looks here ... you gotta wonder, how the heck did the dude not pick up on it any sooner??? He's living/sleeping with her -- and yet, she appears to have been able to keep this one under wraps until it was time to let everyone know.

Obviously, her sisters were probably in the know about her bun in the oven -- and considering how much she's showing ... maybe even Shanna Moakler was privy to it too ... as she claims she has been for weeks. If that's the case -- well done keeping it on the DL.

As you know ... this would be Kourtney's fourth child -- she has three others with her ex, Scott Disick -- and it marks Travis' third. They've hinted at wanting kids of their own since getting hitched ... following a whirlwind romance that ultimately became a fairy tale.