Captain/Jarvis
I cannot say how Mr. Stark will react. I suspect there is no easy way to respond to that type of news, so it might take time. But I think ... Mr. Stark might understand to an extent. He was temporarily hypnotized by a HYDRA agent and nearly killed a great many people. Not that he would admit to it weighing on him, of course. My sympathy goes to your friend. It sounds like none of you came out of the war with what you deserved.
That was me being ... impolite to him. We're in a tiff, as my wife likes to say. I never tiff with her, because she automatically wins by default. But my loyalty will always be to Howard Stark, even when I occasionally want to slam a door in his face. Whatever he feels about this situation, I support him. But I will let your friend tell him, and wish for the best.