Lead surgeon Emmanuel Ameh told the BBC the operation to separate Goodness and Mercy Martins at the chest and abdomen took place in November and the two sisters were now well enough to go home.

He said the operation, which cost about $55,000 (£42,000), was complicated and lasted for about 12 hours. It involved 78 doctors working in two groups.

But the medics at National Hospital Abuja did not charge for their work because the twins’ parents - Michael Edeh and Maria Onya Martins - could not afford the medical bills.

They rely on Mr Martins’ salary as a painter to get by.

The couple had first brought their daughters to hospital in Nigeria’s capital, Abuja, in August 2018 just after their birth.

The children had to wait until they were stronger to be seperatedImage caption: The children had to wait until they were stronger to be seperated

But the doctors couldn’t operate on them immediately as they were not well enough.

They were cared for at the government-owned hospital for the next 15 months and their strength built up over time. The green light was then given for the operation.

The doctors decided to operate a few months after the twins turned oneImage caption: The doctors decided to operate a few months after the twins turned one

The hospital has separated about 11 conjoined twins over the last 20 years, but in those cases all the twins had been joined at the abdomen.

The hospital’s medical director, Jaff Momoh, said this case stood out as it was the first time an operation had involved the lower chest wall, liver and diaphragm.

Mr Martins said he was so happy to see his daughters alive and well - and the family were looking forward to returning home.

His wife said words were not enough to thank the team of doctors and the kindness of the hospital staff.

She said she had felt heartbroken when the babies were born, but now she was all smiles.

The minister of health has visited the hospital to praise the efforts of the medics and meet the family - and the women's affairs minister has promised to give Mrs Martin a job to help the family.