He really shouldn't tell her. It would be, not just unpleasant—he'd do it in a heartbeat if it were merely going to be unpleasant—but counterproductive. She is less likely to take the threat seriously once she discredits the source.

And yet.

"The night before last, Tony was disturbed at his studies by an apparition with the voice and image of Obadiah Stane and no solid physical form. It first tried to pretend it was in fact Obadiah, did not succeed, and proceeded to taunt him as Obadiah and then as each of his parents. He called me about all of this. The next morning—" he breaks off, digs his fingers into his arm, continues with rapidly dwindling steadiness: "The next morning it visited me. In my bedroom. As Obadiah. It was waiting for me when I woke up."