Kate Upton -- UNREAL Sports Illustrated Swimsuit Cover Leaks to Web

The secret is out ... and so is the RIDICULOUSLY SMOKIN' HOT photo ... Kate Upton has been awarded the prestigious title of 2012 Sports Illustrated Swimsuit Edition cover girl.

TMZ has learned ... a few of the issues arrived early to a gas station in Michigan ... and the pics are already making the rounds at breakneck speed. Props to @willdefries for the heads up.

S.I. was originally scheduled to announce the cover girl and reveal the cover shot at an event tonight ... but now, the cat is out of the bag.

We called S.I. about the early release ... but reps for the mag had no comment.