Dean was trapped in 1944. You and Sam were trying to find everything to get Dean back into your timeline. Once you had finally gathered everything, Sam said the spell at the right time and got Dean back.

Dear Lord..

You had never seen a man look so damn fine in a suit. With Dean in his 1940s attire, his slick, combed back hair, and the vest? God. Dean looked at you with a relieved smile, clearly happy to be back.