NEW YORK -- It's a story almost too incredible to believe: Two sisters who didn't know the other existed -- until they found each other by chance when they both signed up for the same college course.
Lizzie Valverde and Katy Olson still marvel at the coincidence, the luck, the fate.
"It feels like a fairy tale," Valverde said.
Their sibling story began when both signed up for a writing course at Columbia University in 2013. Neither could have imagined the tale they would end up telling -- together.
It started on the first day of the class as students were introducing themselves. Something clicked for Olson when Valverde started describing her background.
"And then when she followed up with the rapid fire of more detailed personal questions like, 'Were you given up for adoption in Tampa, Florida, to a woman named Leslie?'" Valverde said. "I was, like, woah woah woah!'"
"The room kind of froze," she said. "And I just said, 'Is this real life?'"
Valverde had already found their mother, Leslie Parker, a few years earlier.
"If you didn't believe in a higher power before you hear this story, you absolutely have to believe in one now because it's basically a miracle," Parker told CBS News by phone from Rhode Island.
Parker was just a troubled teenager when she gave the girls up for adoption at birth, a year apart. Thirty-five years later, her voice still breaks.
"I wanted to give them the best possible future they could have, and it wouldn't have been with me as sad as it is to give up your own children," Parker said, "but I felt that's the best that I could give them is to let them go."
In the next few days, the mom who gave her girls a selfless gift will meet Olson for the first time.
The family's next chapter begins Monday, when Valverde graduates from Columbia with a degree in creative writing -- with her long-lost mother and sister by her side.
"A lot of sacrifices were made for me to be sitting where I am right now, the largest sacrifice, conceivably, ever," Valverde said. "And so, I never forget that."