Sasha Mitchell -- Cody From 'Step By Step' ... Dude, I'm Gettin' Divorced!

Bad news for the Lambert family ... the guy who played Patrick Duffy's surfer dude nephew Cody on "Step By Step" has filed for divorce ... TMZ has learned.

Sasha Mitchell -- whose character (now that we think about it) was essentially a Keanu Reeves ripoff -- filed court docs in L.A. seeking to end his 4 year marriage to his wife Rachel.

The two have no kids together. Sasha blames the split on irreconcilable differences.

Dude, you can finally bang Dana!!!

(Update: Dana's actually married now. Sorry brah)