A Michigan man has given his girlfriend's grandmother an irreplaceable gift: a life-saving transplant.

Last month, Cody Corwin, 26, gave a portion of his liver to 71-year-old Bernice Ramsey. Both are now recovering and Ramsey's family couldn't be more grateful to Corwin and his generosity.

"I am speechless...for him to step up and do something for someone I love so much. I just love him so much more for it," Ramsey's granddaughter Shelby Platt, 26, told "Good Morning America." When she got sick I got really selfish because I kept thinking about her missing my wedding. He saved her life and I'm forever thankful."

Ramsey, a mother of two and grandmother of four, was diagnosed with steatohepatitis, a non-alcoholic fatty liver disease, five years ago. Her brother and sister had died from the disease, Ramsey's daughter Heather Platt, 48, told "GMA."

"The disease causes fat to build up in her liver, which can cause liver failure," said Heather Platt of Chelsea, Michigan, adding that her mom needed a transplant but no one in her family was a match.

Corwin and Ramsey's granddaughter have been dating for three years. When he heard that Ramsey was in need of a liver transplant, he didn't think twice about getting tested since he shared the same O positive blood type.

"She got really sick and she's always been one the sweetest ladies I've ever met," Corwin told "GMA." "When I found out no [family member] was a match I called the Cleveland Clinic [medical center] and found out I was."

He added, "I felt like it was something I had to do for her."

On Feb. 25, Corwin and Ramsey underwent surgery. Despite some hurdles, Ramsey's liver is now functioning well. Corwin said he's also doing well and hopes to return to work in late May.

"How do you thank somebody?" Heather Platt said of her daughter's boyfriend. "For Cody, he had so much to lose. There's a lot that can go wrong. There's no guarantees and for him to be so selfless and say, 'I'll do this for you'--it just means the world to us."