Karmelo Anthony -- the teenager who allegedly stabbed and killed a 17-year-old at a high school track meet back in April -- has been officially charged with first-degree murder.
Collin County District Attorney Greg Willis announced the news just minutes ago ... explaining a grand jury indicted Anthony earlier Tuesday.
The 17-year-old athlete, as you know, has been accused of taking the life of Austin Metcalf during a dispute over a seat at the University Interscholastic League's (UIL) District 11-5A championship on April 2.