Arnold Schwarzenegger's son just scored another major bodybuilding victory, taking home the INBA Iron Gladiator Classic Physique title.

Joseph Baena flexed his way to the top at the California competition Saturday, even snagging his pro card in the process. He celebrated on IG with some gladiator-style flair ... posing onstage with a sword and shield like he just conquered Rome.

Not bad for his second competition ever. Baena made his bodybuilding debut a week ago at the NPC Natural Colorado State show, where he already cleaned up with multiple first-place finishes.

Baena's been all in on the grind, saying this was the year he stopped overthinking and finally committed to competing. And it's clearly paying off.

Of course, having Arnold as your dad doesn't hurt. The bodybuilding legend has been helping Joseph train and fine-tune his posing at Gold's Gym in Venice Beach.

Joseph's been open about struggling with his weight growing up, even getting cut from sports teams and teased by friends ... something that ultimately pushed him toward fitness.