Should I tell him this important thing?

[Wardo94]

I would most likely tell him the truth. When the time was right and what not. Seeing the situation in perspective of you not having any business in telling him this information, it would be disrespectful. That is, if your aunt was planning to tell him in the first place. But she's broke that bond of responsibility. At this point, he deserves to know the truth. Go by how ever you want to go by with it, but if he does ask again, I think it's best to sit him down and tell the truth. If not that, suggest a DNA test to him, if you don't want to personally tell him.