They lovingly call her "mom Oprah."
Oprah Winfrey may not have biological children, but thanks to the first graduates of the Oprah Winfrey Leadership Academy for Girls, she said she now understands the trials and tribulations, as well as the joys, of motherhood.
"We're texting all the time," Winfrey told "Nightline" in an exclusive interview. "I was on the phone last night for an hour with one of them."
The maternal bonding began five years ago, when she handpicked 72 underprivileged girls out of thousands of applicants from shantytowns across South Africa to leave their homes for an opportunity at a top-notch education -- an idea inspired by Nelson Mandela.
"What is the single, life-changing, trajectory-changing moment for me was being exposed to a world of education that offered me insight into how I saw the world, and I just wanted to do that for somebody else. That's all," Winfrey said.
Five years later, six of the girls are in colleges in the United States. Like any proud mom sending her kids off to college, Winfrey said she got emotional over the idea of furnishing their dorm rooms.
"The very first morning that the girls from the United States were here and we were going-- I can't believe I'm weeping over Target and Bed, Bath and Beyond," Winfrey said. "But the morning that we were all getting dressed to go shopping at BBB for their college dorms, I mean, it just [was] the moment it hit me that all the pain, really, and challenges, and difficult circumstances, and the crisis we went through in 2007, and all the questions and times I thought about, 'Give them the money and step out of this and let them have it,' it all came to a head, a joyous fruition."
According to Forbes magazine, Winfrey has devoted $400 million to the girls' education in the U.S. and abroad. Her emotional journey involved in building the school is chronicled in a documentary called, "The First Graduating Class: Oprah Winfrey Leadership Academy for Girls," a two-hour special that will air on the on OWN, Sunday at 9 p.m. ET.
Winfrey said she wanted to make a point of donating not just money to fund the Leadership Academy project, but also her time and energy. In the process of going back and forth to South Africa, Winfrey said she developed meaningful relationships with the girls, who had experienced the struggles of living in poverty -- not unlike Winfrey, herself, who grew up poor and attended segregated schools in Mississippi.
To this day, Winfrey said, she will stop whatever she is doing to take a call or answer a text message from them.
"I'm in a really, really, really good space," Winfrey said. "I will tell you what has brought me the greatest happiness -- so really, really unexpected. Being able to step into the mother role and be a real mother friend companion advisor, comforter to these girls has added another level to my life that really just came as a surprise to me. I didn't really know that I would love it so much."