Dating

How should I go about this?

This is kinda a complicated situation and am not sure how to go about it. There this family friend that I know of and am very interested in getting to knowing him more and see where it goes. The issue is everyone thinks I know this person already which is not true and they do not know that, I do not want that getting out though. I am very serious about knowing more about this person. I was thinking about direct messaging on instagram but i'm not sure if it will be seen since account is private and i do not think this person is active all the time, but thats the only way to reach out. Im nervous that this person will either get annoyed or block me. I am very serious about knowing more about this person. If I do direct message him I was thinking about saying we have a-lot in common and i would like to get to know him more. I was thinking about saying how I know of him but i do not want my extend family finding out since they already think we know each-other help! I really want this to go somewhere with this person!

How should I go about this?
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