After the whole defeating God and Dean dying and quitting hunting thing, Sam married Eileen. You were Dean's kid with an angel. Your mother had taken you away after all that to go live some normal suburban apple pie white picket fence life. Which you absolutely hated.

So, you ran away, going all over the country, all over the world. And, then, in some random diner in some random town, you ran into Sam. Though it took a hell of a lot of convincing, he convinced you to come home with him. Which meant staying with him, Eileen, and their baby son, Dean. Your cousin, who you weren't thrilled about at all.

Sam came in and sat next to you on the couch. "So, Dean's just upstairs, in his nursery," He told you. "If you wanted to meet your baby cousin."