Tyler Christopher, famous for his work on "General Hospital" and "Days of Our Lives," is dead.

The soap star died Tuesday morning in his San Diego apartment, the result of a "cardiac event" ... according to his 'GH' costar Maurice Bernard.

Tyler's being remembered by Maurice as "a truly talented individual that lit up the screen in every scene he performed and relished bringing joy to his loyal fans through his acting."

Maurice continues ... "Tyler was a sweet soul and wonderful friend to all of those who knew him. Tyler was an advocate for better mental health and substance use treatment who openly spoke about his struggles with bipolar depression and alcohol."

Tyler famously played Nikolas Cassadine and Connor Bishop on "General Hospital" ... appearing in 1,153 episodes from 1996 to 2016.

In addition to his longstanding role on 'GH,' Tyler also played Stefan DiMera on "Days of Lives" ... appearing in 160 episodes from 2001 to 2019.

Tyler was 50.