Abbie Greene was given up for adoption on the day she was born in 1948, and she grew up wondering about her true identity.
When she was 17, Greene became obsessed with a news story about a brown-haired baby girl who was found in a cardboard box on the day before New Year's Eve in 1965. She had been left in the laundry room of an apartment building that was just a few miles away from Greene's home in Minneapolis.
"I couldn’t get enough information about that baby," Greene, 67, tells PEOPLE. "I was glued to the TV news, I was reading the papers every day and then the story just stopped."
Greene wouldn't hear any more news of that baby – dubbed "Holly Day" by the nurses who cared for her – until 2014, when she discovered the amazing truth that they were sisters.
Three years prior, Greene had submitted her DNA to 23andMe, a personal genomics website that provides health and ancestry data, in the hopes of finding clues about her biological family.
After years of searching, Greene finally found a close family match in 50-year-old Liz Kellner of Urbana, Illinois.
"I realized quickly that she was my sister and I was just overjoyed," Greene says.
That was just the beginning of their amazing connection. Nearly one year after Greene and Kellner reunited, they found another sister, this time through DNA submitted to Ancestry.com. In August 2015, Greene matched with Tammy Makram, a 54-year-old who shares a biological mother with both women.
Courtesy Liz Kellner / Tammy Makram
Before reaching out to her new sister, Kellner, did some sleuthing and discovered that she and Makram had more than just a biological mother in common. She found a Facebook post in which the Luverne, Minnesota, woman wrote about being discovered in a cardboard box at St. Paul, Minnesota's Miller Hospital as an infant on Christmas Eve in 1961.
"I read her story and her words were mine," says Kellner, who also shares a biological father with Makram.
Last October, the three sisters met for the first time, bringing their friends and adoptive families along for a special reunion in Minneapolis.
"It was one of the best days of my life!" says Greene.
Adds Makram, "There was an overwhelming feeling of love and connection."
Courtesy Liz Kellner & Tammy Makram
For all three women, the meeting brought answers to questions they had grappled with for half a century. Even though they all grew up in loving and supportive families, each one felt a deep longing to better understand themselves and why they were given up.
"You see parts of yourself in each of the siblings," says Makram. "Getting to know them has helped me understand why I am the way I am."
Makram and Kellner are especially grateful for the connection since it has brought some comfort to the painful knowledge that they had been left behind in cardboard boxes, while Greene was given to an adoption agency.
"We are the two that were left, so our experience of growing up and whatever that knowledge did to our psyches, that's something we share," explains Kellner.
"Meeting Liz was the first time that anyone could understand where I was coming from," adds Makram. "After all that time I spent thinking I would never find anyone, to find not just someone who has the same beginnings as me, but a full sister is really amazing."
Courtesy Liz Kellner & Tammy Makram
The three women were able to track down their biological mother, now 87 and suffering from dementia. She and her husband (Makram and Kellner's biological father) have always been reluctant to talk about the past, so much about the sisters' births remains a mystery.
"At this point, she's 87, so it's hard to tell what's repressed versus what's dementia versus there's no way in hell I'm going to talk about this," says Kellner.
However, in coming together they've found a way to accept that some questions may never be answered.
"She gave us up, which was the right thing to do," Kellner says of her biological mother. "We understand that there is a negative side to this story, but we all choose what we make of things, and the fact that we managed to find each other – and that we now have the chance to make up for 50 years apart – is just amazing."
Greene is still searching for her biological father and all three sisters believe there could be more siblings out there. No matter what the future holds, they're grateful to have found each other.
"Finding my birth mother changed my life," Greene says. "But finding sisters was even better."