Lamar Jackson paid a surprise visit to a young fan before the Ravens' big game on Monday -- and the little boy was so moved by seeing the QB in person, he cried tears of joy!!

The heartwarming moment happened just before Lamar beat the New Orleans Saints on "Monday Night Football" -- when the Ravens star snuck into a room to say hello to Landon, one of his biggest fans.

You can see in video of their interaction, filmed by Landon's father, the boy was so shocked to see the former MVP in the flesh -- he ran over to hug him, and wouldn't let go!!

At one point during their embrace, the kid even began crying hysterically.