Eddie Griffin -- The Walk-In VEGAS Wedding!!!!

"Undercover Brother" is officially a married man ... TMZ has learned Eddie Griffin tied the knot in Las Vegas on Thursday after dropping $199 at a walk-in wedding chapel!!!!

Griffin and his fiancee Nia Rivers rolled into the Vegas Weddings chapel on Thursday afternoon -- where they took the plunge in front of 4 guests.

We're told the couple was in a "playful mood" -- and appeared to be very much in love.

Sources say the Griffins splurged on the Cherish Package -- which includes limo transportation, a bouquet for the bride, a boutonniere for the groom and 9 photos.