pat haddison, firefighter, badly burned in the line of duty, endured the most extensive face transplantver attempted. it required a selfless act on the part of a grieving mother. over a year later nancy millar is coming face to face with the man whose bravery made this moment. here's my "nightline" coanchor juju chang. >> reporter: just up those stairs is a man nancy millar has never met. >> what's going through your mind? >> reporter: but his face she already knows. >> i'm going to try not to lose it. >> reporter: it belongs to pat haddison, recipient of a ground-breaking face transplant. >> there's no way to describe the thanks and the gratitude that i have. >> reporter: the donor, nancy's son, david. tonight she's going to meet some of the people whose lives he saved and come face to face with pat for the very first time. >> it's going to be emotional on both ends. >> no more tears. happy tears, happy tears, happy tears. >> here i come. >> all right. >> now i believe we have candles -- >> reporter: it's been more than a year since nancy lost her son dave. >> grab a couple of bouquets