Conor McGregor Jr. Baby Photo, Mean Muggin' For Daddy!

Here he is ... Conor McGregor Jr. ... and the kid is already killin' social media.

Conor McGregor posted the very first pic of his new baby early Sunday morning -- a kid with steely eyes and a tough lookin' jaw. Kid's got a big right arm, too.

He'll clearly destroy all other babies in the maternity ward.

The UFC superstar's girlfriend Dee Devlin looks great -- smiling with the kid at Coombe Maternity Hospital in Ireland, where the baby was born Friday night.

By the way, Conor Jr. is already proving to be a massive hit on social media -- with more than 40,000 followers on Instagram in the first 48 hours of his life.