In that case I think you would need to make a judgment based on your knowledge of your friend, whether he is already strong in emunah and would appreciate hearing the emes even if it bursts his bubble, in which case it might be good to tell him.
Otherwise I would leave it alone because even though its a good midda to seek the emes, it’s not an aveira to believe in something that is not true but also not against Torah hashkafa, so I’m not sure it is worth causing him tzaar or risk shaking his emuna before he’s ready for it.