Seventeen-month-old Max Matthews has given his nine-year-old sister Megan the ultimate gift: a cure for a life-threatening disease.
In doing so, he has became the first 'saviour sibling' to be created in the UK, after doctors cultivated embryos that could provide stem cells to treat Megan's condition.
Max was conceived through IVF to be a genetically selected match suitable to transplant bone marrow to his sister.
After he was born, blood taken from his umbilical cord and bone marrow was successfully used in a transplant for Megan, who suffers from Fanconi anaemia and was not expected to live beyond seven years old. The condition predisposes sufferers to diseases such as cancer and leukaemia.
While 'saviour siblings' have been born before with the help of US laboratories, this is the first time medics have carried out the entire process in the UK.
Opponents have argued that screening embryos and creating 'designer' babies to save a sibling's life meddles with nature and risks turning children into commodities. But the Matthews family, from King's Lynn, Norfolk, reject the criticism.
'There is no question that we have done the right thing,' said mum Katie, speaking in the Daily Mail.
'Max completed our family and gave his sister the chance of a normal life. It has triggered a really special bond between them – they are always together and it is lovely to see.'
Megan's only chance of a cure was a bone marrow transplant, but checks on her older brother Stuart, 11, who is free of the disease, and the world bone marrow register, failed to find a match.
'We always wanted three children' said Katie. 'The only reason we didn't have another child after Megan was that there was a one in four chance we could pass the disease on because both me and my husband are carriers.'
The couple underwent IVF, funded by the NHS, which decides funding in these circumstances on a case by case basis.
The embryos were screened and suitable ones selected using a process called Pre-Implantation Genetic Diagnosis – the first time it has been carried out in Britain. The result was Max, born on July 22 last year.
By the time stem cells harvested from Max's umbilical cord and bone marrow were transplanted into his sister at Bristol Royal Hospital for Sick Children in July this year, every day was a battle for her.
Repeated infections meant she was in and out of hospital. She needed a blood platelet transfusion twice a week, full blood transfusions every two to three weeks and had to be wired up to a pump for 12 hours every night to try to clear her blood of high levels of iron.
But since the transplant, Megan has made astonishing progress. She was in hospital for just eight weeks and is doing so well she may be able to stop taking some of her medication early next year.
Megan said: 'I feel so much better and can't wait to do normal things. Soon I will be able to start swimming and dancing again and I have just been on my first sleepover.'
Mum Katie said: 'We can't thank everyone enough.'
'It has been a tremendous rollercoaster of highs and lows but Megan is now making fantastic progress, better than we could have hoped for. For the first time we are looking forward to Christmas without worrying whether Megan will be well or not.'