Chapman responded immediately when she learned her friend would need a new kidney.
"OK, well, take mine," she texted Dudley. "I have two. You need one."
Testing showed that both young women have the same blood type, O-positive.
"We've been friends for pretty much forever," Dudley told the news station. "Turns out we're not just best friends, but our antibodies are, too."
The friends are doing so well that doctors anticipated discharging Chapman on Thursday. Dudley could go home as soon as Friday.
Word of the friend's unique situation got out when Chapman's father and Grant's first husband, singer-songwriter Gary Chapman, requested prayers on his Facebook page Monday night.
“They’ve known each other their entire lives and, when Kathryn was in need, (it) turns out Millie was a perfect match,” Gary Chapman wrote. “I’m so proud of her, words fail me.”
He updated his followers after the surgery, telling his fans that both young women were doing well.
“Millie is out of surgery and everything is looking good. She’ll be hurting for a while, but healing is underway,” he wrote.
Grant also posted the news Wednesday on her Facebook page, saying that she and her family were "so proud of Millie's selfless act of friendship, and (we) are grateful that both girls are doing well after yesterday's surgeries." WKRN reported that Grant had barely left the hospital during her daughter's stay, and Gary Chapman was seen Wednesday helping Millie walk up and down the hallways.
Grant and Gary Chapman, who divorced in 1999 after 17 years of marriage, have three children together. Grant also has a 15-year-old daughter with her second husband, country singer-songwriter Vince Gill.