3:21 PM PT -- 'Talladega Nights' director Adam McKay says he's "heartbroken and stunned" over Houston's suicide.
Adam's remembering Houston as a "joyful and talented person" and says he will never forget the good laughs and good times they shared.
Houston Tumlin, who starred as a child actor 15 years ago in 'Talladega Nights,' has taken his own life.
Houston shot himself in the head inside his home in Pelham, Alabama around 4:30 PM Tuesday ... Shelby County Coroner Lina Evans tells TMZ.
We're told Houston's girlfriend was inside the home at the time of his suicide ... and so far, no note has been found.
Houston is best known for playing the foul-mouthed, 10-year-old Walker Bobby, son of Will Ferrell's character Ricky Bobby, in the 2006 comedy, "Talladega Nights: The Ballad of Ricky Bobby."
His character had a ton of memorable moments and lines in 'Talladega Nights' ... like the famous dinner scene opposite Grayson Russell as Texas Ranger Bobby.
The hit movie is Houston's only acting credit ... and as recently as 2015 he was reportedly serving in the Army's 101st Airborne Division at Fort Campbell. He also worked other jobs, like repairing telephone lines.