Jack Piney Jr. is one of only 800 people in the world to have been diagnosed with Systemic Juvenile Xanthogranuloma Histiocytosis.
He was in hospital from the day he was born and his diagnosis meant he was put on the UK's liver transplant list at five months of age.
Medical experts said he had only weeks to live after a month of waiting for a donor, so his dad, Jack, gave them permission to carry out ground-breaking surgery in order to save his son's life.
Surgeons took 12 hours to extract part of Jack's liver, attach it to his son's circulatory system and reduce it to fit his tiny body.
The little boy lost all of his blood three times during the operation, but his dad was glad that they took it on.
Jack Sr said: "Donating a section of my liver to my son was by far the most amazing thing I have ever done.
"Donating my organs after I die will, I'm sure - will be a close second."
Obviously, he couldn't have thanked the surgeons enough for what they achieved.
He said: "Apparently the two surgeons didn't speak more than 10 words to each other during the entire thing. They are really amazing men.
"I couldn't thank them enough and they were extremely humble."
Little Jack has since been doing amazingly well, according to his Facebook page Jacks Story - Living with a liver transplant.
.