the woman who helped save him. really? yes. oh, my god. reporter: bob overcome. oh, my god. reporter: it turns out kerry wasn t a complete stranger. she actually learned from her brother that his father-in-law needed help so she got tested to see if she was a match. and right here tonight hi, david. reporter: kerr roin why she did it. i m going to be bob s kidney donor, because i could not see a reason not to. reporter: and tonight, the most graceful person of all, bob. especially after that moment at the back door. now i know my life will last a lot longer. i ll be strong every. and it will be a lot better for my life. an extraordinary gift. good night.