Angelina Jolie and Brad Pitt’s son Knox Jolie-Pitt went from cap and gown to gloves and kicks in the span of a few hours ... celebrating his high school graduation before stepping into the ring for a Muay Thai fight later that same night.

The 17-year-old surprised classmates and parents during a graduation speech Friday in Los Angeles when he revealed he'd be competing after the ceremony. Knox even joked to the crowd that he was going to "knock 'em" out ... drawing cheers from the audience.

Waiting for your permission to load the Instagram Media.

A proud Angelina was spotted snapping photos as her son took the stage ... then later showed up to support him as he traded his diploma for fight gear and squared off against an opponent in the martial arts exhibition.

Footage from the event show Knox exchanging punches and kicks in a spirited showdown -- and this wasn't his first trip to the ring. As TMZ previously reported, the youngest son of Jolie and Pitt has become seriously involved in Muay Thai and won a competition in Los Angeles last year, with Angelina and twin sister Vivienne cheering him on from ringside.

Knox has largely stayed out of the spotlight compared to his famous parents, but his fighting skills have been turning heads lately ... and drawing comparisons to Brad's shredded "Fight Club" days.

Looks like Knox isn't wasting any time figuring out life after high school ... he's already throwing punches at it.