78-year-old runner describes moments after Boston Marathon explosions

78-year-old Bill Iffrig was just about to cross the finish line at the Boston Marathon when two explosions knocked him to his feet. 

A picture of him on the ground was captured by a Boston Globe photographer. That photo is now going viral. 

The veteran marathoner described what the moment was like to CNN's Pier Morgan. 

He said, "I was just approaching the last straight-away to the finish line and I had a good day and was feeling really good, and I got down to within about 15 feet of the finishing apron and just tremendous explosion, sounded like a bomb went off right next to me, and the shock waves just hit my whole body and my legs just started jittering around. I knew I was going down and so I ended up down on the blacktop and I didn't feel any severe pain but as I rolled over, I seen a little scratch on my leg but nothing too bad, so I laid there just momentarily."

He went on to tell CNN that a race official helped him off the ground and carried him across the finish line so he could finish his race. 

Iffrig says someone offered him a wheelchair but he didn't need it. He was able to walk back to his hotel. 

This was Iffrig's third time running in the Boston Marathon.