The moment your mom, Helena, passed away, your world changed drastically. You were sad, hurt, angry. She has been ill for years, and you knew that, eventually, she would have left you. During the last moment you spent with her she gave you a letter that you read just a few days after her funeral.
In that letter she told you how much she loved you and how you'll have to learn to move on without her. "You are 18 now, you are big and strong. You'll do it without me too"... and she also wrote down the truth about your dad, the dad that you never met, the dad that she never mentioned. You did want to know the truth, but you never really asked her anything. She was enough for you, you didn't need anyone else.
She wrote down that your dad is called Spencer Reid and that he works for the FBI. She just met him once and that's why she never told him anything about you. She was too scared of telling him even because of his dangerous job and because she didn't know if he would have stick around for you two.
You thought about your mom's words for a while, and eventually you decided to go to Virginia to meet your dad. You read lots of things about him: he is a genius, ha has an eidetic memory, he had three PhDs and he is still working for the FBI while also making some time to work as a Professor at University. Since you don't know where he lives, you decide to show up at the FBI quarters.
You walk to the reception desk, asking for Spencer Reid. But as soon as you say so, you hear someone talking behind you. "That would be me." He says, looking at you, clearly confused. He walks closer to you. "Do I know you?" He asks, still in a kind tone.