The pair fell in love but, two months later, Robbins, then 24, was told he had to quickly leave for the Eastern Front. Later back in the US, he got married to someone else.
"I told her maybe I'll come back and take you, but it did not happen like that," Robbins told French television channel France 2.
"When he left in the truck, I cried, of course, I was very sad," Pierson said. "I wish after the war he hadn't returned to America."
When the war came to an end in 1945, Pierson began learning basic English phrases, hoping Robbins would one day return for her.
It was there he met and married Lillian, his wife of 70 years. They worked alongside each other in a hardware store in Mississippi for 50 years. She passed away in 2015 at the age of 92.
Pierson also fell in love again. She got married in 1949 and became a mother to five children.
Despite marrying, Robbins kept a black and white photo of his wartime sweetheart.
When he returned to France for this month's D-Day anniversary commemorations, he was clutching the image, unsure if she was still alive.
He assumed that Pierson had passed away, saying: "For sure I won't ever get to see her."
Robbins met some French journalists who helped track her down and organise an emotional reunion.
Robbins and Pierson immediately embraced when they were reunited, gazing into each other's eyes with adoration and joy.
"I always loved you. You never got out of my heart," Robbins told Pierson.
"He said he loves me. I understood that much," Pierson told one of the journalists in French.