How to inform one's parents about a possible disorder their child has?

A year ago, I started dating this guy with ADHD. It was a very troubled relationship, but I realized that it was not due to his ADHD. I highly fear that he has a Narcissistic Personality Disorder. I have more than enough data to confirm it to the point it's beyond obvious and non arguable. I read books, articles, journals, everything relating to the disorder and ADHD. People with ADHD are likely to have a comorbid disorder like NPD and most NDP patients have ADHD.

While him and I separated because our relationship was unbearable, I know that he will keep hurting his surroundings like he hurt me and it will get worse with age. He is currently 19 and this sort of disorders only manifest itself in early adulthood. I feel like it's the time to help him while he is still young. Everyone knows there is something odd about him, but I doubt anyone managed to really define it. They just assume he's just special.

Do you think I should inform someone about the possibility of his condition?

Should I even inform anyone, or is it none of my business?