Dean had kept it together just for long enough to explain it to the kid, because Ben deserved to know, and then he waited, watching Ben to see what his reaction would be.
He didn't have to wait long, because after a mere moment that felt like an eternity later, Ben was whooping and dancing and Dean felt like doing the same. Somehow it had all worked out and the test was back and Ben was his son. It was almost dizzying, like getting drunk on really expensive alcohol instead of the cheap strong stuff, all the things that this meant. Was Ben going to want to be called Ben Winchester? Was he supposed to act differently now, more 'dad like?' Was he going to have to start doing discipline and laying down ground rules? It was easy to overlook the fact he had already had more than one serious talk with Ben before, because that was in the past, before he knew he was a dad. It felt daunting, impossible, and yet like Christmas all at once.
Before he knew it, Ben was back, and calling him Dad (which was, to be honest, something Dean never thought he'd hear anyone call him) and throwing himself at Dean. Dean latched on hugging the boy--his son, Dean realized with a grin--tightly.
"Hey, son." he said, voice unusually deep and rough with emotion.