'The Sopranos' star died at age 51 from a heart attack last week, sending shock waves in Hollywood.
Breaking her silence on her friend untimely passing, Stewart said she had fond memories of working with the actor in 2010 indie drama, reported Entertainment Weekly.
"When I heard of James' passing I was in New Orleans, where we met shooting, and every memory flooded back and gutted me," said Stewart.
"I'll hold that time near to me forever. He was immeasurably great. My heart goes out to his beloved family."