She literally gave a part of herself to her best friend to save her life.

Gloria Mills "Millie" Chapman—the 27-year-old daughter of Contemporary Christian Music artists Amy Grant and Gary Chapman and the inspiration behind Grant's Grammy-winning hit "Baby Baby"—donated her kidney to her best friend, Kathryn Dudley, on Jan. 24, the Tennessean reported.

Both Amy and Gary expressed great pride at what their daughter had done, posting their separate messages on their Facebook pages.

Amy, who was reportedly at the hospital during the surgeries, posted on Facebook that she was so proud of her daughter's "selfless act of friendship."

Gary was also at the hospital during and after the surgeries and was seen helping his daughter Millie walk down the hall.

On his Facebook page, he wrote, "I'm so proud of her, words fail me."

Millie's stepsister and Vince Gill's daughter Jenny Gill also posted on her Facebook page, saying she's "in awe" at what her stepsister has done, calling it "an act of true love."

One day after the surgeries, Kathryn said she could not thank her friend Millie enough.

She recalled that at the age of 13 she was diagnosed with FSGS (focal segmental glomerulosclerosis). "The parts of the kidneys, the tubes, they scar, so I basically just kind have little tiny rocks for kidneys. They don't work," she told WKRN.

In 2014, she said her doctors told her the only option left to keep her alive was kidney transplant.

She then texted Millie, telling her that she's in kidney failure. At that time, Millie was miles away in New York City.

"I was at a Yankees game, and she just said she was going into active kidney failure," said Millie. She said she replied, "OK well take mine, I have two, you need one."

During the matching test, the two proved to be a match, both with an O+ blood type.

"We've been friends for pretty much forever," said Kathryn. "Turns out we're not just best friends, but our antibodies are, too. She'll forever be a part of me."