Couple Seeks Stranger Who Snapped 'Perfect' Shot of NYC Marathon Proposal

He came, he ran, he proposed, he ran some more.

That is the summary of Joe Duarte's proposal to Katie Mascenik in the middle of the New York City Marathon, and now the New Jersey couple is on the hunt to find the "perfect" photo that a bystander snapped of their engagement.

Duarte and Mascenik are both fitness instructors and running enthusiasts. They have run three marathons and more than 20 half marathons together all over the world, the couple said, and their love of running has been a significant aspect of their relationship.

When Duarte signed up for the NYC Marathon, Mascenik said she didn't expect it to turn into something more than a long run. Mascenik told ABC News that although the couple had discussed wedding plans in the past, Duarte had told Mascenik not to expect a ring until January of 2016, which is why the bride-to-be had no idea that a proposal was coming as she waited at Mile 17 to cheer Duarte on.

When Duarte ran up to Mascenik, the fitness trainer just expected him to give her a quick kiss and then continue on with the race. Instead, Duarte dropped to one knee and popped the question. Mascenik, of course, said yes.

"I was totally surprised," Mascenik said.

After the proposal, Duarte continued running the race, and Mascenik started heading over to Mile 24 to meet up with her new fiance. By the time she realized that a bystander had taken the perfect shot of the proposal, it was too late to go back and look for her.

Now, the couple is sharing their story in hopes of finding that "perfect" photo from their engagement, to have as a memory of their special day, Mascenik said.

Mascenik posted a photo to her Facebook page of the proposal moment, taken from a slightly different angle. Specifically, the couple is looking for the photo taken by the person in the foreground.

"Running means so much for us and it would just be fantastic to have," she said.