(Kevork Djansezian/AP Photo)

Sage Stallone, son of actor Sylvester Stallone, was found dead in his apartment today, ABC News Los Angeles station KABC reported.

He was 36.

The cause of his death was not clear.

"I'm devastated. He's an extremely bright, creative person," Sage Stallone's longtime attorney, George Braunstein, told KABC.

Sage Stallone played Rocky's son, Robert Balboa, in "Rocky 5." He also appeared in the film "Daylight" with his father Sylvester Stallone.

Sylvester Stallone's publicist Michelle Bega told the Associated Press that the actor is "devastated and grief-stricken over the sudden loss of his son."

"His compassion and thoughts are with Sage's mother, Sasha," Bega said in a statement.