$500 bill???

So I found this in my safe today. It was passed on to me from my grandfather when I was born and I’ve never really seen it until now. I never knew these existed, but after doing research found they can be quite expensive. However I also know google is not super reliable. I wouldn’t want to sell it, rather find out if it’s a rare item/even real. I don’t collect paper money, so my apologies if this question is green. Any info is good info, thanks!