Usain Bolt Introduces Smokin' Hot Girlfriend

Sorry ladies, Usain Bolt's taken ... and his girlfriend is an absolute smoke show!

Bolt is usually pretty quiet about his relationships -- but his rep confirmed the world's fastest man is dating Kasi Bennett ... a fashionista who also rocks the hell out of a carnival bikini.

In fact, the two were spotted kissing out in public during a parade in New Kingston back in April ... and he recently referred to her as his "First Lady" in an Instagram post.

Hail to the chief ...