I like my brothers friend.. ?

So it all started when i was on Facebook a couple months ago, and my brothers friend messaged me asking me a question. now you should know my brother and him had split apart since they were younger. Me and him started talking a lot to the point that we are flirting now. Here's the thing, i'm not sure if he knows i'm my brothers sister and i feel like it would be weird if he knew because i was annoying af when i was younger. Do you think he knows ? should i tell him. (p.s him and my brother are starting to talk again+we are 3 years apart).
I like my brothers friend.. ?
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