"I was pushing a stroller, had a diaper bag on my arm and also lugging an oxygen machine for my daughter," Zwick wrote, according to USA Today.
"We pre-boarded the plane, got cozy in our window seat and made jokes to those around us about having to sit by my yelling-but-happy baby."
"The flight attendant came over and told me you were waiting to switch seats," Zwick recalled. "You were giving up your comfortable, first class seat to us."
"Not able to hold back tears, I cried my way up the aisle while my daughter Lucy laughed! She felt it in her bones too... real, pure, goodness," she continued.
"...Thank you," she wrote to the then-unidentified man. "Not just for the seat itself but for noticing. For seeing us and realizing that maybe things are not always easy. For deciding you wanted to show a random act of kindness to us."
"It reminded me how much good there is in this world. I can’t wait to tell Lucy someday," Zwick concluded. "In the meantime... we will pay it forward."
Not long after her Facebook post went viral, however, Zwick shared that the owner of the first class seat reached out to her. “I guess it was his birthday, and he did reach out to us,” Zwick shared with Yahoo News. “He was thanking me for a birthday to remember. It was the best day. He said [the Facebook post] made him and his wife cry, and he said, ‘I am so glad we were on the same flight.’”