Sylvester Stallone is reportedly in shambles over the loss of his child.

The actor's 36-year-old son Sage was found in his Los Angeles apartment by either his girlfriend or a maid on Friday July 13.

Sage was pronounced dead at the scene. He reportedly died of a pill overdose.

Sylvester was hit hard by the news.

"This came completely out of the blue," said a source.

"Sylvester did not see this coming for one minute. Sage was healthy, and Sylvester thought he was doing really well, this came from complete left field."

Sylvester and Sage starred together in Rocky V and Daylight in the mid 1990s.

The pair had a strong relationship and Sylvester can't believe he's gone.

"Sylvester was very close to Sage and he is absolutely overwhelmed with grief by his death," the source continued. "He is totally stunned and still in a state of shock."

Sources claim that police are still trying to determine whether Sage's cause of death was accidental or intentional.