It depends as some deaths by illnesses are hereditary.
If you are perhaps alluding to suicide, then yes as it may concern me that a member of my family who I knew very well (talking in actuality here) and who was the happiest person ever on the outside, could be driven to do such a thing to himself and those around him.
So yes, it probably matters quite a lot. And I would wonder why it was a 'secret'.
I would also go over things like 'why was it a secret' and really, as we dont know the details, it does depend on the circumstances and nitty-gritty.
Good luck Mini, i'll be thinking of you.
Whatever it was though, dont dwell. Let it out of you with a bucket of ice-cream for a day if needed but it was 9 years ago and as long as you are not in danger now accept and move on. Could you speak to other family members about it?