Nate Diaz is a daddy!!!

The 33-year-old UFC superstar and his longtime girlfriend, Misty Brown, welcomed a healthy baby girl at a California hospital on June 6 ... according to public birth records obtained by TMZ Sports.

Nate and Misty -- both from Stockton, CA -- have been together for years. They've been posting photos of each other online ... dating back to 2012. 

We're told the baby is happy and healthy, and the families are stoked. 

We reached out to Nate's camp for comment -- but a call to the fighter's rep was not returned. 

Congrats!