Nathan Shorey, three, has been diagnosed with acute lymphoblastic leukaemia, and if his condition deteriorates, he may need a stem cell transplant.
The boys' parents, Melanie, 34, and Michael, 36, are hopeful Samuel's stem cells can be used to help Nathan if needed in the future.
"When we were told Nathan had leukaemia, it was heartbreaking," says mum of four, Melanie. "As soon as you hear the word leukaemia, you fear the worst. Nathan is currently doing well and I do try to remain positive, but there is the worry in the back of my mind that his condition could relapse.
"Samuel's stem cells have been tested and are a match for Nathan so can be used if needed. Nathan absolutely loves Samuel and there is a special bond between them.
"The chance of Nathan relapsing is thought to be low, but when I found out that stem cells could be taken from the umbilical cord I felt it was the right thing to do."
Nathan was diagnosed with leukaemia in 2010. He was in hospital for the first six months after diagnosis, but is now doing well after 19 months of maintenance chemotherapy.
What do you think about Samuel's stem cells potentially being used to treat Nathan?