When one man offered to take a stranger's baby so she could rest on a recent flight, many people on the plane watched in awe.

"It was so uplifting," one passenger, Andrea Byrd, told TODAY. She snapped a photo of the man carrying the baby up and down the aisle and posted it on Facebook, where it's since gone viral.

"I was in tears," Byrd wrote in the post, which has been shared almost 100,000 times. "Not because he was white and she was black... but because it showed me today that there are still good people out there in a world full of turmoil."

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The Southwest Airlines flight was heading from Minneapolis to Atlanta on Sept. 5.

The mom, Monica Nelson, who is pregnant, told TODAY she had been nervous about traveling alone with her 20-month-old son Luke. When he grew fussy and wouldn't rest, the man seated next to them surprised her by offering to help, she said. He walked up and down the aisle holding the boy, soothing him to sleep.

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"It was such a relief because I was a little worried traveling with him without my husband there to help out," said Nelson, a teacher who lives in Atlanta. "I'm still very grateful — he was so kind."

She said the man's name is Reid, and she learned that he also has a son named Luke.

Byrd said she was particularly touched by the scene because she has two children of her own and could put herself in the mom's shoes, and that's what moved her to snap the photo and post it online.

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"He just kind of swooped in," she said. "You usually don't see things like that. It was so sweet."

Now their story has touched thousands of people across the world, reminding people how powerful a simple act of kindness can be.

"It's good to know the world is not all bad," Nelson said. "There are some really great people out there."

This article was originally published on Sep. 9, 2016 on TODAY.com.