Lee Thompson Young -- 'Rizzoli & Isles' Runs On-Air Tribute to Fallen Star

Just one day after learning of his death, Lee Thompson Young's co-stars on the TNT show "Rizzoli & Isles" paid homage to the fallen actor with an on-air tribute.

At the end of the show Tuesday night, a title screen appeared with the words, "In Loving Memory of Lee Thompson Young 1984-2013" ... followed by two silent clips of the 29-year-old actor.

We broke the story ... Young's body was discovered inside his North Hollywood apartment Monday morning ... after producers called the actor's landlord to check up on him when he failed to show up on set for work.

Officials say Young took his own life ... but it's still unclear why.