PHILADELPHIA -- For approximately 30,000 runners, Sunday's Philadelphia Marathon was a life-changing experience. That is especially true for John Allen and Amy Duncan of Harrisburg, Pennsylvania.

"The surprise showed me just how much I was loved by my best friends," bride-to-be Shelby Nelms told Newsweek.

I planned the greatest surprise proposal I could dream of - and it turned out even more magical than I imagined. In this video, I take you behind the scenes of every detail: the setup, the nerves, the ...