Mr Andy Toh, 49, would not be celebrating Christmas this year if Mr Ralph Chua, 42, had not given him part of his liver.
The duo had been colleagues at Paya Lebar Methodist Church for about a decade, but knew each other only casually as they were in different departments.
Mr Toh, a father of two teenagers, was thus surprised when Mr Chua visited him in hospital in March. He was even more surprised when Mr Chua said as he was leaving: "If you need a live donor, let me know."
Mr Toh had felt a range of emotions - from shock to hope, anger and despair - after he was diagnosed with late-stage liver failure in October last year. By then, his liver was badly scarred and hardening as a result of hepatitis B.
His wife, siblings and 18-year-old son were all found to be unsuitable as donors. Only his daughter Bernice was a match.
Although scared, she wanted to help. But at 16, she was too young as donors had to be at least 21.
Dr Thwin Maung Aye, a consultant at the National University Centre for Organ Transplantation, said Mr Toh also had complications such as recurrent fluid accumulation in the tummy. His "overall prognosis and survival would have been poor" if he did not have a transplant, he added.
On May 15, the transplant was carried out. Dr Thwin said Mr Toh responded very well and his other medical problems were resolved after the liver transplant.
The operation left Mr Chua with less than half of his liver, but this usually regenerates.
While Mr Chua, who does multimedia work, was not close to Mr Toh, who is from the discipleship and nurture department, he said he felt obliged to help as he had a friend who died from liver cancer.
That Mr Chua had four young children aged one to nine years old, and had just committed to a new executive condominium unit, did not stop him. His wife was anxious but supportive when he told her he felt it was a calling from God.
"The doctor said, looking at the shape of my liver, it's like I was born to donate," he recalled.
Last week, the two families got together at Mr Chua's new flat in Pasir Ris for an early Christmas celebration.
Mr Toh's wife Angelia, a teacher, said the family lost all hope before they heard that several people had offered to donate part of their livers. She did not know who they were, but was grateful.
Mr Chua said: "Christmas is also the time for giving and appreciating friends and family. It brings great joy to know both Andy and I are well after the operation."