12:16 PM -- Conor McGregor just shared some pictures of he and Dee Devlin's newborn son ... saying, "Another chunky healthy boy into the world. Dee you are my hero ❤️🙏"

The future of MMA has arrived -- Conor McGregor and his longtime partner, Dee Devlin, just welcomed their fourth child together!!

Notorious shared the big news just minutes ago ... saying, "My baby boy is born! Mammy and baby doing amazing, 8.1lbs of prime Irish double champion beef! ❤️🙏"

The McGregor family hasn't revealed the new youngin's name just yet ... but that'll come in due time.

Of course, Conor and Dee share three other kids together -- Conor Jr. (6), Croia (4) and Rian (2).

McGregor announced the addition to the family back in June ... and even then, he was super stoked about being a papa of four. In fact, the champ-champ was spotted kissing Dee's baby bump during a beach day back in August.

The UFC superstar gave his millions of social media followers a heads-up on Wednesday ... saying they were prepping for the big arrival first thing in the morning.

We're sure Conor can't wait to get the kid in the gym -- after all, Conor Jr. is already picking up on the craft!!

Congratulations to the family ... and look out, future fighters!!