5:44 AM PT -- 4/23 -- NBA star Donovan Mitchellwas super close with Clarke and considered him a "little brother."
Mitchell posted a video of one of their last conversations, which happened to have been captured by Slam Online, showing how they would joke with each other about basketball and life.
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"We’ve had too many convos like this bro," Mitchell said.
"One thing I can always say bro is your energy was unmatched your vibe was always lit! You were like a Lil brother to me bro just trynna make it to the league live your dream help moms out! You were so close bro so close!"
"I appreciate you for being a dope friend to my little sister man this hurts to even have to write! Rest in paradise lil bro! Gone to soon."
Terrence Clarke -- a 19-year-old University of Kentucky basketball player and a projected 2021 NBA Draft pick -- was killed Thursday in a car accident in Los Angeles, law enforcement sources tell TMZ Sports.
We're told Clarke was driving a Genesis around 2 PM in the San Fernando Valley when his vehicle was struck by another car ... sending him smashing into a pole and before ultimately slamming into a wall.
Footage from the accident shows Clarke's vehicle completely smashed in.
Law enforcement sources tell us the accident is being investigated -- but so far, no official cause of the crash has been determined.
We're told Clarke was in Los Angeles with his Kentucky teammate, B.J. Boston -- another NBA Draft prospect.
Boston was reportedly in the car behind Clarke when the accident occurred -- but we're told he's physically okay.
Clarke was rushed to a nearby hospital ... but injuries proved too severe and doctors were unable to save his life. He was pronounced dead shortly after arriving at the hospital.
Terrence -- a 6'7" guard -- was an absolute stud on the hardwood. Rivals rated him a 5-star recruit coming out of high school in New Hampshire ... and ranked him as the #8 overall high school player in the entire country.
He didn't play much at Kentucky -- but he clearly had the talent to succeed at the pro level and recently declared for the 2021 NBA Draft.
Some experts projected he would be a 2nd-round pick -- with tons of upside.